Why Do Galaxies Collide, While Stars Almost Never Do

Multiple Choice

Why do galaxies collide, while stars almost never do?

A) stars have a very strong negative charge on them, so they repel other stars that get near
B) stars don't have very much mass, so their gravity is very small and can't pull things well
C) stars are much further apart (compared to how big they are) than galaxies are
D) stars are surrounded by planets, which prevent collisions; galaxies are not
E) actually, stars collide all the time, but astronomers don't have any way of observing it