1. It cannot be said that
the stabiliser will always produce negative lift (a down force)
2. The question does state in the cruise, and to improve efficiency an aft CG
is better than a fwd CG, so an up force can be
produced contributing to the total lift force if the CG is behind the
aerodynamic centre.
3. Flaps will increase downwash and if the tail is ice covered its stalling
alpha would have been reduced so there is a strong possibility it could stall.
4. The horizontal stabiliser is there to stabilise the longitudinal axis of the
aircraft, by balancing the pitching moment of the wings, fuselage engines?
So from the options given 2, 3 & 4 are correct.