The is grammatically incorrect.

• The sentence has an error in it. Let us find where the error is residing.

• In the first part of the sentence the subject is mentioned which is my friends.

• The subject is followed by the main verb 'moved'. The sentence is written in the simple past tense as the subject has taken the house some time ago.

• Now only the last part of the sentence is left. Here we can find the object along with an article and a preposition. Article 'the' the is applicable here because a particular location that is a sea, is mentioned here. When we try to figure out a particular thing or incident we use 'the'.

• Here the proposition is only left. The preposition at is used to indicate time or any specific location in cities or villages.

• The preposition by is used to indicate someone has done something. To express the doer of the action we use this preposition especially in the passive sentences. We can also use 'by' to mention 'next to' or 'beside'.

• The sentence in the question will take 'by' as the preposition of the object. The subject has a house beside the sea. So, the most convenient and useful preposition will be 'by' instead of 'at'.

• Thus, the correct sentence will be:

My friends moved to a small house by the sea.

• Hence, option A is the correct answer.

Option B has the grammatically incorrect part. The error is in the use of the word "scenery".

• The word "scenery" is a noun. 
  
  
• It means the general appearance of the natural environment, especially when it is beautiful.
  
  
• We do not need a noun here.
  
  
• For the noun 'route', we need an adjective to describe it.
  
  
• Thus, replace "scenery" with "scenic" to make the sentence grammatically sound.

Option B has the grammatically incorrect part. The error is of the tense. 

• The first part of the sentence tells us that the vaccine is yet to reach India.
  
  
• Thus, it will only be made available in the future.
  
  
• Thus, we will use the future tense.
  
  
• So, replace 'is' with "will be" to make the sentence grammatically sound.

Thus, the correct sentence will be: US drugmaker Moderna’s covid-19 messenger RNA vaccine is likely to reach India this week and will be available in a few major government hospitals by the middle of this month.

The sentence is grammatically incorrect and the error lies in option C.

• The error is related to the verb "give".
  
  
• The given sentence is in past tense.
  
  
• The simple past and the past perfect express completed actions that took place in the past.
  
  
• We use the simple past to say what happened in the past, often in sequential order.
  
  
• The past perfect expresses events and actions that occurred prior to another past action (usually expressed in the simple past).
  
  E.g. :- When he woke up, his mother had already prepared breakfast.
  
  
• So, the verb should also be in past form i.e. gave (second form of the verb ‘give’).
  
  
• In order to make the sentence correct, replace "give" with "gave".

Thus, the correct sentence will be: ‘She had already fastened her seatbelt when the flight attendants gave the safety demonstration.’

The sentence is grammatically incorrect and the error lies in option D.

• The error is related to the preposition "on".
  
• Prior to’ means before a particular time or event or before something or coming before in time, order, or importance. 
  E.g. :- All utensils should be washed prior to use.
  
• We usually use preposition ‘to’ with ‘prior’.
  
• In order to make the sentence correct, replace "on" with "to".

Thus, the correct sentence will be: ‘Passengers may board the plane twenty minutes prior to departure.’

• The error is related to the word "back".

• Call something off means deciding that a planned event, especially a sports event, will not happen, or to end an activity because it is no longer useful or possible or to cancel something.
  • E.g. :-
    1. Tomorrow's match has been called off because of the icy weather.
    2. Jason called the wedding off because he wasn't in love with his fiancé.

• But here, the sentence says that someone returns to the company, but the offices were closed.

• For that, we use the phrasal verb ‘call back’.

• Called back is a phrasal verb which means ‘to return to a place in order to see someone or collect something or to return a phone call’.
  • E.g. :-
    1. She said she'd call back later to pick up that report.
    2. He's going to call back tomorrow night, at exactly 9:00.

• In order to make the sentence correct, replace "off" with "back".

Thus, the correct sentence will be: ‘I called the company back, but the offices were closed for the weekend.’

The sentence is grammatically incorrect and the error lies in option B.

• The error is related to the noun "laziness".

• ‘Unreliable’ is an adjective which means ‘liable to be erroneous or misleading’.

• The conjunction ‘and’ connects similar parts of speech.

• ‘Laziness’ is a noun which means the quality of not being willing to work or use any effort.
  • E.g. :- I could go to the gym - it's just laziness that stops me.

• In its place, an adjective should be used and that will be ‘lazy’.

• ‘Lazy’ is an adjective which means ‘not willing to work or use any effort’.
  • E.g. :-
    1. Get out of bed, you lazy thing!
    2. He's too lazy to walk to work.

• In order to make the sentence correct, replace " laziness" with "lazy".

Thus, the correct sentence will be: ‘Managers had complained that the workers were lazy and unreliable.’

The error is in the segment 'the world heritage site' and it is related to articles.

The definite article (the) is used before a noun to indicate that the identity of the noun is known to the reader. The indefinite article (a, an) is used before a noun that is general or when its identity is not known.

Here, a general group of world heritage sites is mentioned. Hence, 'the' should be replaced with 'a' to make the sentence grammatically correct.

Therefore, option A is the correct answer.

The given sentence lacks parallelism.

Parallelism uses similar words, phrases, or clauses to show that ideas have the same level of importance. It is the use of components in a sentence that are grammatically the same; or similar in their construction, sound, meaning.

The sentence is in the past tense, however, present tense of the verb i.e. 'need' is used. Also, the sentence is in the reported speech.

Therefore, 'need' should be replaced with 'needed' to make the sentence grammatically correct.

Therefore, option C is the correct answer.

The error is in the segment 'is penalize' and it is related to form of verbs. We use participle after 'be' form of the verb.

Also, Rohit has got punishment from someone. Therefore, the sentence is in the passive voice.

Hence, 'penalize' should be replaced with 'penalized' to make the sentence grammatically correct.

Therefore, option D is the correct answer.