Answer:
a) Before the plane is directly over the target
Step-by-step explanation:
When a crate would be dropped from the cargo plane, its initial vertical velocity would be zero (free fall) but it would still have horizontal velocity of the moving plane. Therefore, the falling crate would transverse a parabolic path.
In order to make it hit the target, the crate should be dropped before the plane is directly over the target because of the horizontal component of net velocity will take the crate towards the target.
Thus, option a is correct.