Question

which sentence is in passive voice? significant improvements in athletic performance have been documented by dr. robertson’s studies. dr. robertson’s studies have documented significant improvements in athletic performance.

Explanation:

Passive voice structures place the receiver of an action as the subject, using a form of "to be" + past participle, with the doer often introduced by "by". The first sentence has "improvements" (the receiver of the documenting action) as the subject, uses "have been documented" (be verb + past participle), and names the doer "Dr. Robertson's studies" with "by". The second sentence uses active voice, with the doer "Dr. Robertson's studies" as the subject performing the action "have documented".

Answer:

Significant improvements in athletic performance have been documented by Dr. Robertson's studies.