This is an imperative sentence. In such sentences, order, request, advise or negative command is given. In negative command, the reported speech starts with Do not or Don't.
Rules for changing imperative sentences in indirect speech:

• Say/said to changes to order/ordered/command/commanded/request/requested/urge/urged/advise/advised/ask/asked/tell/told/suggest/suggested as per the sense of the sentence.
• Inverted commas (" ") is removed and to is used before the main verb.
• The pronoun of the reported speech changes accordingly.
• The words like kindly, please are removed.
• For negative command, inverted commas are removed and not + to + verb (first form) is used. For example, “do not go” changes to “not to go”.
• In negative commands, forbid/forbade + object + to + verb (first form) is also used.

Common rules for direct/indirect speech:

• The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

Rules for changing the direct speech into indirect speech are given below:

• The inverted commas (“ “) used in Direct Narration is removed in Indirect Narration and “that” conjunction is used.
• Says to/said to changes to tells/told in indirect speech if they are followed by an object. If not, they would remain same in indirect speech.

How to changes the tense in indirect speech

• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech.
• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.
• Can, shall, will, may, must changes to could, should, would, might and must respectively.
• If there are any universal truth, habitual fact in the reporting speech, no changes are made to the reported verb’s tense.

How some words change in indirect speech

• Words like “this, these, tomorrow, yesterday change to that, those, the next day, the previous day” respectively.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

The word “let” is used to suggest, to propose or to allow something. Below are the rules for changing such sentences in indirect speech:

• Say/said to changes to propose/proposed; suggest/suggested.
• If the reporting verb has an object, then it is used with “to” after proposed/suggested.
• The inverted commas (“ “) used in is removed and “that” conjunction is used.
• “Should + verb (Ist form)” is used after subject of the reported verb.

• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.
• The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

Rules for changing the direct speech into indirect speech are given below:

• The inverted commas (“ “) used in Direct Narration is removed in Indirect Narration and ‘that’ conjunction is used.
• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech.
• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present changes to simple past.
• Present continuous changes to past continuous.
• Present perfect changes to past perfect.
• Present Perfect continuous changes to past perfect continuous.
• Simple past changes to past perfect.
• Past continuous changes to past perfect continuous.
• Can, shall, will, may, must change to could, should, would and might respectively.
• If there is any universal truth, habitual fact in the reporting speech, no changes are made to the reported verb’s tense.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

Rules for changing imperative sentences in indirect speech:

• Say/said to changes to order/ordered/command/commanded/request/requested/urge/urged/advise/advised/ask/asked/tell/told/suggest/suggested.
• Inverted commas (" ") is removed and to is used before the main verb.
• The pronoun of the reported speech changes accordingly.
• The words like kindly, please are removed.
• For negative command, inverted commas are removed and not + to + verb (first form) is used. For example, do not go changes to not to go.
• In negative commands, forbid/forbade + object + to + verb (first form) is also used.

Common rules for direct/indirect speech:

• The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

Rules for changing the direct speech into indirect speech:

• The inverted commas (“ “) used in Direct Narration is removed in Indirect Narration and “that” conjunction is used.
• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech.
• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.
• Can, shall, will, may, must changes to could, should, would, might and must respectively.
• If there are any universal truth, habitual fact in the reporting speech, no changes are made to the reported verb’s tense.
• Words like “this, these, tomorrow, yesterday change to that, those, the next day, the previous day” respectively

Rules for changing the direct speech into indirect speech for interrogative sentences:

• Said/say is changed to ask/asked/wonder/wondered/enquire of/enquired of.
• Inverted commas (" ") are removed.
• If the reported speech is in YES/NO question form then if/whether is used before reported speech.
• If the reported speech is in the form of WH-Question (who/what/why/how/where/when/which etc), no conjunction is used before the question word. The question word itself works as a conjunction.
• Reported verb is made assertive; i.e. it is kept in the order of subject + verb.
• The sign of interrogation (?) is removed and full stop is used.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

The given sentence is in Indirect speech. So, we must apply the rules in reverse order to change it into Direct speech. Or we can see the options and find the Direct speech whose Indirect speech is the given sentence. 

“Requested” shows an act of asking politely or formally for something. So, the Direct speech will have the word “please”.

Option A: “He said” is incorrect reporting pronoun as the request was made by "my friend" and not "he".

Option B: This is an interrogative sentence, so, it is incorrect as the meaning of the sentence is changed.

Option D: “said he” is incorrect reporting pronoun as the request was made by "my friend" and not "he". Also “bring my friend a sandwich” is incorrect use of words.

This is a direct narration of an exclamatory sentence. We change such sentences in indirect narration using the following rules:

• Said is changed to exclaimed/exclaimed with joy/exclaimed with sorrow/ exclaimed with grief/ confessed with regret/ shouted with applause/ cried out/ eagerly wished.
• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech. In such cases, says to changes to tells/comments.
• Inverted commas (" ") are removed and that is used instead.
• The verb and tense of the reported speech changes accordingly.
• Sign of exclamation (!) if given is removed and full stop is used.

Now, we can find the answer by analysing the options:

Option B: “how well” is incorrect use of words as per the above rules.

Option C: The given sentence is in present tense, so there will be no change in the reported verb. “Sang” is incorrectly used in option C.

Option D: The meaning of the sentence is changed. Also, the given sentence is in present tense, so there will be no change in the reported verb. “Sang” is incorrectly used here.