Discuss how the choice of angle for maximum range of a projectile would be affected by the resistance of the air to motion of the projectile through it.

If the drag force is greater than the weight of the object, the air resistance will have significant effect on the range of the projectile. The air resistance experienced by the object is directly proportional to the instantaneous velocity. Therefore when the object moves with high speed, the air resistance would increase.
The velocity of the object, when it falls from some height, under the influence of air resistance is given as:

It is clear from this equation that the velocity of the object reaches its terminal velocity as the time t proceeds. Therefore the object acceleration in the vertical direction does not stay constant as it used to when no air drag exist. This breaks the symmetry of the projectile and the range of the object decreases significantly.
The similar thing happens when the object in projectile motion moves upward. However, the drag force and the weight of the object are in the same direction now, and also accounts for the reduced maximum height of the object.