Which of the following statements about asteroids is true?
A. Asteroids are all very large and are mostly made up of stone, iron and nickel.
B. Asteroids vary greatly in size and are mostly made up of frozen water and gas.
C. Asteroids vary greatly in size and are mostly made up of stone, iron and nickel.
D. Asteroids are all very large and are mostly made up of frozen water and gas.