Which of these is true for a glider flying with constant angle of attack?
Two things are important here:


It is about a glider, so no fuel is consumed, and the mass is constant over time.
The angle of attack is constant. This means also that the lift and drag coefficients are constant.


If the mass and the lift coefficient are constant, and we assume a constant load factor (implied by the gliding along its path description), the dynamic pressure is also constant, and the airspeed changes with the square root of air density. Gliding implies that the altitude decreases, so the indicated speed will be constant, but the true speed will decrease. Unfortunately, the condition e) is not precise enough to make this distinction. e) could be correct or not, depending on the definition of V.

I would suggest that also c) could be a correct answer: If the angle of attack and the mass are constant, so should be the drag coefficient. However, gliding down also implies that the Reynolds number changes because true speed decreases and temperature increases over the glide. Strictly speaking, this would also mean a very slowly changing drag coefficient.

Answers b) and d) are false and I agree with your reasoning.