Question

An interjection is used to
A. modify a noun.
B. modify a verb.
C. express emotion.
D. separate clauses.

Answer 1

An interjection is used to c. express emotion.

Some examples are "hey", "well", "oh", etc. An interjection usually goes at the beginning of a sentence and is usually used with an exclamation mark.

Hope this is helpful~

Answer 2

C. express emotion.
This is because a interjection is when you are emotional expressing something.
Like:
Hey!
Or Oh!