He does not know how to use . . . . . . . . smartphone.

A. the

B. an

C. some

D. a

Answer: Option D

Solution(By Examveda Team)

Articles are used before nouns or noun equivalents and are a type of adjective. The definite article (the) is used before a noun to indicate that the identity of the noun is known to the reader. The indefinite article (a, an) is used before a noun that is general or when its identity is not known.