Conservation of Momentum: a Small Glider Is Coasting Horizontally When

Conservation of momentum: A small glider is coasting horizontally when suddenly a very heavy piece of cargo falls out of the bottom of the plane. You can neglect air resistance. Just after the cargo has fallen out

A) the plane speeds up and the cargo slows down.
B) the plane speeds up but the cargo does not change speed.
C) neither the cargo nor the plane change speed.
D) the cargo slows down but the plane does not change speed.
E) both the cargo and the plane speed up.