A space station orbits the Earth with constant speed. What can be said about the space station's acceleration?
a. It is zero because the space station moves with constant speed.
b. It is greater than 9 . 8 m / s 2 because the space station is moving so quickly.
c. It is less than 9 . 8 m / s 2 because the space station is so high above the Earth's surface.
d. It is equal to 9 . 8 m / s 2