Question

when a writer does not know who performed the action in a sentence, the writer can still write a grammatically correct sentence by
○ using the active voice.
○ using the passive voice.
○ ending the sentence with an infinitive.
○ ending the sentence with a preposition

Explanation:

In grammar, the passive voice is used when the doer of the action (the agent) is unknown, unimportant, or we want to focus on the receiver of the action. Active voice requires knowing the subject (doer) of the action. Ending a sentence with an infinitive or a preposition is a matter of sentence structure/style and not related to handling unknown agents. So the correct choice is using the passive voice.

Answer:

B. using the passive voice