Anoun or a pronoun that follows another noun or pronoun in a sentence to identify or explain it is called a(n)

gerund

appositive

infinitive

A noun or a pronoun that follows another noun or pronoun in a sentence to identify or explain it is called an appositive.

Explanation: An appositive is a noun, a noun phrase or a pronoun added to a sentence in order to rename another noun or pronoun and clarify its identity. The noun or pronoun modified by the appositive is found right beside it, that is to say that the noun or pronoun modified by the appositive generally precedes the appositive. There are two types of appositive: restrictive appositives and nonrestrictive appositives. Appositives are restrictive when they offer essential information and there are no commas around them. In contrast, appositives are nonrestrictive when they do not present relevant information and there are commas around them.

i would say the correct answer is not concrete.

c) problem and solution