What causes an airplane (except a T-tail) to pitch nosedown when power is reduced and controls are not adjusted?
A. When thrust is reduced to less than weight, lift is also reduced and the wings can no longer support the weight.
B. The downwash on the elevators from the propeller slipstream is reduced and elevator effectiveness is reduced.
C. The CG shifts forward when thrust and drag are reduced.

Answer (A) is incorrect.
Thrust and weight have no relationship to each other.B.
The downwash on the elevators from the propeller slipstream is reduced and elevator effectiveness is reduced.

Answer (A) is incorrect.
Thrust and weight have no relationship to each other.

Explanation of correct answer:
Airplanes (except a T-tail) normally pitch down when power is reduced (and the controls are not adjusted) because the downwash on the elevators from the propeller slipstream is reduced and elevator effectiveness is reduced. This allows the nose to drop.