The shape of the earth's orbit around the sun is essentially a circle. assuming the earth maintains a constant speed as it orbits around the sun, which statement about the earth's motion is most correct?

select one:
a. its acceleration is zero since it is moving at constant speed.
b. its acceleration is not zero but is very small.
c. its acceleration is 9.8 m/s2.
d. its acceleration is 1.0 m/s2.