A flashing white light directed at an aircraft on the manoeuvring area of an airport means
Why this is the answer
Per the TC AIM tower light signals, a flashing white light directs an aircraft on the manoeuvring area to return to its starting point on the airport — it is not a taxi clearance or a stop signal.
Reference
TC AIM-RAC – Visual Signals
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.