Reflecting telescopes are popular because they're
a. more durable than a refracting telescope.
b. easier to build than a refracting telescope.
c. more powerful than a refracting telescope.
d. smaller than a refracting telescope.

The answer is letter C.

Reflecting telescopes are more powerful than refracting telescopes. These are also called as reflectors which serves an optical telescope that uses a single or combination of curved mirrors. These mirrors then reflect light and form an image. It is designed for very large diameter objects and are mostly considered as major telescopes in the field of astronomy. They were used as an alternative for refracting telescopes during the 17th century because they suffer less chromatic aberrations than a refracting telescope does.