Which of the following sentences contains a demonstrative adjective?

A. This hat is his.

B. Whose is this?

C. This is his.

D. Which one is this?

Answer:A and C

Explanation:they both modify the noun of a thing that is being referred to

A: This hat is his.

Explanation:

The sentence "This hat is his" contains a demonstrative adjective: This. The purpose of a demonstrative adjective is to modify a noun or pronoun, and it will come right before the noun or pronoun. In this case, the noun is hat. The same word "this" that appears in B, C and D is a demonstrative pronoun, which comes alone and doesn't modify a noun.