Which term describes large groups of stars, dust, and gas?

• A. Sun
• B. Solar system
• C. Nebula
• D. Galaxies

Answer: (D)

The idea here is recognizing structures by their scale and content. A galaxy is a gravitationally bound system that contains vast numbers of stars, plus gas and dust, spanning enormous distances. That combination—many stars with a shared reservoir of gas and dust bound together—defines a galaxy.

In contrast, a sun is just one star, a solar system is that star with its planets, and a nebula is a cloud of gas and dust, often a birthplace of stars, not a bound collection of many stars. So the term that best fits “large groups of stars, dust, and gas” is galaxies.