When Space Probe Voyager 2 Passed by Saturn,its Speed Increased

Multiple Choice

When space probe Voyager 2 passed by Saturn,its speed increased (but not due to firing its engines) .What must have happened?

A) Voyager 2 must have dipped through Saturn's atmosphere.
B) Saturn's rotation must have sped up slightly.
C) Saturn must have lost a very tiny bit of its orbital energy.
D) Saturn must have captured an asteroid at precisely the moment that Voyager 2 passed by.