The radius of the earth is
a. not known.
b. the same everywhere.
c. larger at the poles.
d. larger at the equator.

It is D. Larger at the equator, This is because the Earth isn't a perfect sphere; it bulges around the equator because it's rotating on its axis. The Earth is a flattened sphere, and so the distance around the equator is further than the circumference around the poles.