The underlined part of the sentence is grammatically incorrect. After an article, we must use a noun. ‘Complain’ is a verb, the noun form is ‘Complaint’.

Also, the correct verb to use with ‘complaint’ is “file” which means “submit a legal document or application or charge, to be placed on record by the appropriate authority”. We ‘fill’ a form and ‘file’ a complaint or charge. As the sentence is in past tense the verb will become “filed”.

The correct preposition to use here is ‘against’ because it follows “filed a complaint” always.

Hence, option B is the correct answer.

The underlined part is grammatically incorrect. Thus, the best suited is “nightmares had been vague, with”.

Hence, option B is the correct answer.

The underlined part is grammatically incorrect. The correct phrasal verb to be used here is ‘asked after’ and not ‘asked to’.

Ask after: It is used to say that you would like to know how somebody is, what they are doing.

Ex: Mother always asks after my roommate.

Thus, ‘to’ should be replaced with ‘after’ in order to make the sentence correct.

Also, the correct determiner to be used should be ‘elder’ and not ‘older’ as ‘elder’ is used to represent the family. 

Hence, option D is the correct answer.

The underlined part is grammatically incorrect. First of all, ‘many + of’ should be followed by the objective form of the pronoun.

For example:
Many of them were ready to put up a fight.

So in the sentence "we" must be replaced with "us", the objective case of the pronoun "we".

Since the subject (many) is plural, it will take the plural verb; thus replace ‘listens’ with ‘listen’. Also, to modify the verb "listen" we need an adverb. ‘happy’ is an adjective and cannot improve a verb, it can improve a noun or a pronoun.

For example:
They lived happily ever after. (Lived = verb)
Let us put on our happy faces. (Faces = noun)

Thus, "happy" should be replaced by "happily".

Hence, option B is the correct answer.

The underlined part is grammatically incorrect. First of all, the singular subject ‘Climate change’ will take the singular verb ‘heaps’ and not ‘heap’. Also, the verb ‘heaps’ should be modified by the adverb ‘disproportionately’ and not by the adjective ‘disproportionate’. This is given only in option C.

Hence, option C is the correct answer.

The underlined part is grammatically incorrect. Since the sentence is in the active voice, the modal ‘would’ should be followed by the first from of the verb ‘listen’ (and not ‘listened’). Also, the noun form ‘advice’ should be used instead of the verb ‘advise’. This is given only in option D.

Hence, option D is the correct answer.

The underlined part is grammatically incorrect. If 'one' is the subject, we must use "one’s" as its possessive adjective. Also, the word 'aware' is an adjective (and there is no such word as 'awared') and it takes the preposition 'of' after it. Hence, option D is the correct answer.

The underlined part is totally correct. There is no need of substitution here. Hence option C is correct.

The underlined segment is grammatically correct. See through something means to realise the truth about something. Hence, option D is the correct answer.