Case of subject-verb agreement. Here we need to keep two things in mind - 1. this is a general statement of fact (present tense), 2. two different subjects are discussed here. Considering these, option 2 seems fit.

Case of subject-verb agreement. 'One of' is always followed by a singular auxilary. Now here option 1 and 3 both are singular, but 'today' in the sentence demands present tense auxilary. Thus, option 1.

This is a general statement of fact (present tense). Two subjects (or nouns) are discussed that demand plural auxilary. Hence, 'bring' is the correct option.

Verb 'carried' shows that this is a fact of the past tense. Now 'luggage' is a singular noun or subject, and it needs singular auxilary. Thus, option 1.

Here clothing is taken as a single piece of dress. And bieng a singular noun, it needs a singular auxilary. Hence, option 1.

Generaslly, one does not live at, in or on post office as the same is not a place to live in. Yes, but one can live near or beside post office. Hence, option 1.

To refer to persons (in subjective cases) we use relative pronoun 'who'.

We live 'in' a house, but we live 'at' an adress.

Here the word 'down' qualifies to the train, which is a noun. And anything that tells about a noun is an adjective.

We live 'in' a house (either big or small), but we live 'at' an adress.

The sentence implies thta this quotation is extracted or taken 'from' the words of Keats.

The sentence implies that he is acceptable to me despite all his faults. For this, preposition 'with' is the best usage.

Here usage of article 'the' with the books specifies that we are referring to some special or particular books. And to show this specification, we prefer relative pronoun 'that' to 'which'.

The word 'either' here qualifies to the noun (bat), and anything that qualifies a noun is an adjective.

'The watch' means some special or specific watch. And whenever we refer to something specific, we prefer relative pronoun 'that' to 'which'.

This is an idiomatic usage, where 'down' is treated as a noun.

This is an adage. Here despite the usage of determiner 'those' we use 'who' rather than using 'that'. This is an exceptional case.

'Ups and downs' here means noun.

Here the word 'either' substitutes the subjects (or nouns), and anything that replaces a noun is a pronoun.

Here the word 'you' is used as a replacement for the person (or noun) who is the doer of the work. And any word that substitutes a noun is a pronoun.

Here children are subjects (but not specified subjects), and for living subjects we use relative pronoun 'who'.

Here the word 'are' is a verb of being as it mentions about the nature of a noun.

Here the word 'them' substitutes the noun 'book', and anything that substitutes a noun is a pronoun.

To leave something is a sort of work. Hence, option 2.