A rocket can fly into space because ?

A. when it is launched, the hot exhaust gases hit the ground and push the rocket forward.

B. the rocket pushes the exhaust gases backward, and there is an equal and opposite reaction pushing the rocket forward.

C. when the gases are burning up, the mass of the rocket decreases, changing the amount of gravity on the rocket.

D. the launch pad pushes the rocket forward like a slingshot.