complete the summary by choosing one sentence (A, B, C or D) that is among the most

A. Variable stars may differ in the amount of energy they radiate or in their luminosity.

B. Variable stars change in brightness and luminosity, and require a telescope with a large lens

C. Proxima Centauri, the closest star to Earth, is a binary star and requires a large telescope for observation

D. Many different types of stars exist, but the most important categories are variable and binary stars.