general physics

In your frame, a certain galaxy is moving at a high speed in the x-direction. Relative to the galaxy, a certain comet in the galaxy is also moving at a high speed in the x-direction. Let a be the galaxy’s speed with respect to you, b be the comet’s speed with respect to the galaxy, and c be the comet’s speed with respect to you. Then

Select one:
a. a + b > c
b. a + b < c
c. a + b = c
d. a 2 + b 2 = c 2