The CARs define an infant passenger as a person
Why this is the answer
Per CAR 101.01, an infant passenger is a person under two years of age. The weight-based and three- or five-year definitions are distractors.
Reference
CARs 101.01 – Infant
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.