A Rocket Obeys the Principles of Recoil

Multiple Choice

A rocket obeys the principles of recoil. However, it is much more difficult to apply Newton's second law to a rocket because

A) Newton's three laws do not apply in outer space.
B) there is actually sideways momentum, because a rocket motor is just a well-controlled explosion.
C) the rocket pushes against air but the air is a fluid.
D) as the rocket motor fires the total mass of the rocket changes.