The universe is often described as "clumpy" with dense groups of matter separated by empty space. A single clump made of billions of stars is known as a

A) galaxy.

B) nebula.

C) light year.

D) solar system.

A. Galaxy. is the correct answer. a galaxy is a colossal grouping of solar systems, and stars that slowly orbit each other, and other galaxies.

B. nebula. is incorrect. a nebula is a large collection of dust and small meteoroids.

C. light year. is not correct. light year - a large unit of distance, often used when measuring the distance between galaxies.

D. solar system. is incorrect. solar system - a group of planets and a star.