The simple answer is that it all depends. It depends on the context - what you are going on to say.
For an easy illustration, instead of a verb, use a hammer as it's much simpler to make up appropriate examples:
The camper used a stone as a hammer to knock the pegs into the ground.
(Indefinite articles before an unspecified items)
The campers used stones as hammers to knock the pegs into the ground.
(No article required before plural items)
The campers used the stones lying around as hammers.
(Definite article before specified items)
The campers used stones as the hammers that were later found with blood marks.
(Definite article before specified objects)
The same rules apply if you were making up sentences with the word verb. So you could talk about:
the word used as a verb
the words used as verbs or
the words used as the verbs that fitted the context.
In your example, the answer depends on the context:
Option A and Option B are used as the verbs expected by the teacher.
Option A and Option B are used as verbs rather than nouns.