Pilots shall activate the transponder “ident” feature
Why this is the answer
Per TC AIM-COM, a pilot operates the transponder 'ident' feature only when ATC requests it, so that the controller can positively identify the intended target.
Reference
TC AIM-COM – Phraseology
Question reproduced verbatim from Transport Canada’s PSTAR Study and Reference Guide (TP 11919E). The answer key is Transport Canada’s; the explanation is ours.
A study aid — not a substitute for the official guide, the CARs, or your instructor.