Answer” Increase of speed generates pull forces.” Is incorrect. If the CG is ahead of the neutral point we will have a stable configuration, so an increase in speed would require a push force.

Answer “Aeroplane nose up trim decreases the stick force stability.” Is incorrect. If you trim nose up, you would have to keep a forward pressure on the stick to maintain straight and level. If you increase speed, the forward pressure would increase as the elevator become more effective, and that is in the same sense you would expect with a speed increase, so stick force stability increases.

Answer “Stick force stability is not affected by trim. “ Is incorrect. If you trimmed nose down you would require a pull force to keep the nose up, and fly straight and level. As you increased speed the pull force would increase, which is not what you would expect, so that is an unstable stick force. So trim does affect stick force stability.
You can calculate the difference of a 10 kt change at low speed and high speed to prove the answer. It goes about the percentage change in lift.
If you assume a CL of 0.3 in straight and level and substitute changes of speed maintaining the same angle of attack, then you will see that the percentage change in lift, and therefore stick forces, will be greater at lower speeds. L = CL x V2 (no change in the ˝ ρ or S so we can leave them out, in this calculation) (I also left it in Kts, as it will not affect this specific calculation, but we should use M/sec)
Change in speed 60 70 120 130
Squared 3600 4900 14400 16900
X 0.3 1080 1470 4320 5070
Change 390 750
Percentage 36% 17%