Wake turbulence caused by a departing aeroplane is most severe immediately
Why this is the answer
Per TC AIM-AIR (Wake Turbulence), a departing aeroplane's wake is most severe just after lift-off, where it is heavy, slow, and at a high angle of attack. Plan to become airborne before the larger aircraft's rotation point and stay upwind of its path.
Reference
TC AIM-AIR – Wake Turbulence
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.