Low Level Airspace is defined as, all airspace
Why this is the answer
Per TC AIM-RAC (High and Low Level Airspace), Low Level Airspace is all airspace within the Canadian Domestic Airspace below 18,000 feet ASL. The options tying it to a height above designated airways describe airways/routes, not Low Level Airspace itself.
Reference
TC AIM-RAC – High and Low Level Airspace
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.