Question

which sentence is in passive voice? an x - ray could have detected the hairline fracture in his arm. the hairline fracture could have been detected by an x - ray.

Explanation:

To identify passive voice, we look for the structure where the object of the action (in active voice) becomes the subject, and the verb is in a form of "be + past participle" (here, "could have been detected"). In the first sentence, "An X - ray" (doer) is the subject performing "detected" (active). In the second, "The hairline fracture" (receiver of action) is subject, with "could have been detected" (passive verb form) and "by an X - ray" (agent of action).

Answer:

The hairline fracture could have been detected by an X - ray.