1. Why is 250 million years called a cosmic year? A: That's the amount of time it takes the solar system to revolve around the Milky way core.

B: That's the amount of time it takes the solar system to rotate on its axis.

C: That's the amount of time it takes the Milky Way to rotate on its axis.

D: That's the amount of time it takes the Milky Way to revolve around the Universe core.