The underlined part is grammatically incorrect.

• Certain verbs take direct V+ing after them. For eg: Avoid, mind, detest, resist, enjoy.

• For example:

They enjoyed riding through the valley.

• Also, Modal “will” expresses a prediction. But the sense of the sentence is about giving advice; hence we have to prefer “should” modal over “will” to improve the mood of the sentence.

• Hence, “should avoid making” is the correct improvement.

Thus, the correct sentence will be: The manager remarked that we should avoid making such small errors in the production stage.

Hence, option C is the correct answer.

The underlined part of the sentence is grammatically incorrect.

• The underlined part has reporting verb “said”. “Said” does not take indirect object directly after it. They are generally separated by preposition “to”.

• Reporting verb “told” takes indirect object directly after it. Hence, it does not need preposition “to” directly after it.

• For example:

Hema said to her aunt, “Please close the close”.

She told us about an amusing event.

• Pronoun “his” is used for nouns of masculine gender. For feminine, “her” is used.

• Also, the proper reporting verb as per the sentence is “ask” since the girl is asking “to explain” something.

• Hence, “asked her mentor” is the correct improvement.

Thus, the correct sentence will be: At the end of the lecture, the inattentive girl asked her mentor to explain the last question again.

Hence, option B is the correct answer.

The underlined part of the sentence is grammatically incorrect.

• The underlined part has verb “is” which is not in accordance with the subject “passengers”. The plural verb “are” should be used for the plural subject "passengers".

• Preposition “for” should be used.

• “To” preposition is used to point towards a direction.

• Moreover, if something is waiting for you, it has been left or prepared for you to collect, use, enjoy, or deal with when you arrive.

• E.g. :- Uma had a cup of coffee waiting for me, along with a plate of biscuits.

• Hence, “are waiting for” is the correct improvement.

Thus, the correct sentence will be: The passengers are waiting for the bus which is widely praised in the city for its exemplary services.

Hence, option C is the correct answer.

The underlined part of the sentence is grammatically incorrect.

• The underlined part has preposition “by” which is wrong since it is used for any medium of transport.

• Preposition “to” should be used which is used for directing towards somebody/some location. Here, it directs/points out to “animal”.

• Also, sentence is talking about “equal effect (fatal) of steroids” over animal and man.

• This is clear from the word “as” used before “man”. So, “as” should be used in place of “enough” in the underlined part.

For example: My sister is as tall as me.

• Hence, “as fatal to” is the correct improvement.

Thus, the correct sentence will be: The recent study shows that an overdose of steroids is as fatal to an animal as to a man.

Hence, option C is the correct answer.

The underlined part of the sentence is grammatically incorrect.

• The underlined part has “his” which is used for noun of masculine gender. For feminine, we use “her”.

• Also, Correlative Conjunctions are used for emphasising the idea of one thing coming immediately after another, for eg: “Hardly.....when” , “No sooner.....than”

For example:

Hardly had Ravi sat down when the phone rang.

• Hence, “her dinner when” is the correct improvement.

Thus, the correct sentence will be: Hardly had she finished her dinner when the mobile phone rang abruptly with a brassy ringtone.

Hence, option C is the correct answer.

The underlined part of the sentence is grammatically incorrect.

• The underlined part has “be+V1” which is wrong since sentence is in passive voice. Hence, “be+V3” should be used.

• Also, “nip in the bud” is idiom which means to stop something when it has just begun. Thus, it is wrong to use preposition “on” in the idiom.

• Hence, “be nipped in the bud” is the correct improvement.

Thus, the correct sentence will be: It is always advisable that immoral and unethical practices should be nipped in the bud to avoid any probable damages in the future.

Hence, option C is the correct answer.

The underlined part of the sentence is grammatically incorrect.

• The underlined part needs the object of the verb “serve”. 
• “Summon” is a verb and a verb cannot be the object. 
• So, we need noun here i.e. “summons”. 
• Please note that though it may appear that “summons” is a plural noun, it is actually a singular noun. It’s plural form is “summonses”
• Also, “in” is a preposition of place which should not be used here. “Against” is the correct preposition. 
• For example: 

They took out a summons against her for noise nuisance. 

• Hence, “summons against him” is the correct improvement.

Thus, the correct sentence will be: The police is unable to serve summons against him over his alleged role in money laundering.

The underlined part of the sentence is grammatically incorrect.

• “Success” is a noun that is the subject complement for the subject “Ravi Kumar Dahiya”.

• We need an adjective phrase to qualify the noun “success”.

• "Due to” is a preposition when used with any Noun/Pronoun makes an adjective phrase. 

• “Owing to” is a preposition when used with any Noun/Pronoun that makes an adverb phrase.   

• Thus, using “due to” is correct here.

• Also, using “its” is wrong here since it is connected with things.

• Thus, “due to his efforts” is the correct improvement.

The correct sentence will be:  Ravi Kumar Dahiya got success due to his efforts.
Hence, option B is the correct answer.

The underlined part is grammatically incorrect.

• The sentence is in the passive voice since the subject (prime accused) is a recipient of a verb's action.
  
  
• “Brought” should be replaced with “was brought”. Also, it is not necessary to mention the doer in passive form when it is implicit.

• We use the preposition "before" (and not "in front of") when the context is around a judge (or court).

• Hence, “was brought before” is the correct improvement.

The correct sentence will be: On Monday, the prime accused was brought before the judge.

Hence, option B is the correct answer.

• The underlined segment is erroneous.

• In the underlined segment, an adverb is used to modify the noun.

• However, an adverb is a word or phrase that modifies or qualifies an adjective, verb, or other adverb or a word group, expressing a relation of place, time, circumstance, manner, cause, degree, etc. (e.g., gently, quite, then, there).

• An adjective is used to modify the noun. Therefore, 'anonymously' should be used instead of 'anonymous'.

• Also, 'ascribed' is always followed by the preposition 'to'.

• For example, he ascribed Jane's short temper to her upset stomach.

• Hence, 'at' should be replaced with 'to'.

• Therefore, the underlined segment should be replaced with 'this anonymous play to' to make the sentence grammatically correct.

The correct sentence would be - After years of research, scholars have finally ascribed this anonymous play to Christopher Marlowe.

Hence, option B is the correct answer.