Choose the noun which is only used in the singular.

In Noun-Number, there are two types of numbers: singular and plural. A noun that refers to multiple individuals or objects is said to be in the plural. Singular Number: A singular noun is one that only refers to one individual or object. Even while singular nouns are usually easy to comprehend, things can sometimes get confusing. For instance, a collective noun is a singular noun that represents a group of individuals or objects as a singular body. Therefore, furniture is a singular noun. Option D is the right answer since some words like advice and hair are only used in the singular.