It is not necessary to use every type of supporting material when researching a topic.
i would say a or c because the others are not corrected sentences. a is correct but it’s not capitalized (the 1st letter) and c could be i instead of me.
what is the antecedent of the pronoun those?
sentence: those are books that need to be returned to the library
pronouns are used to replace nouns with more general terms that don't describe a specific person or place. the antecedent of a pronoun is the word that the pronoun replaces.
in the case of this sentence, the pronoun those replaces the word books, therefore the antecedent of the pronoun those is books.
the theme of universality in town is expressed in ensuring all citizens upon the occurrence of a relevant social circumstance (sickness, unemployment, old age, employment injury, having many children, maternity, disability, loss of the breadwinner, etc.)