A Spaceship and Docking Module Travelling in Parallel Come Alongside

Multiple Choice

A spaceship and docking module travelling in parallel come alongside each other at the same speed. The module fires a small rocket at a right angle to its motion to bring the module into contact with the spaceship for docking. On docking, which one of these effects does this have on the motion of the combined craft?

A) none
B) Their speed decreases.
C) They acquire a small component of velocity perpendicular to the original motion.
D) They continue with increased velocity in the same direction.