Which statement is the best description of the Milky Way galaxy? OPTIONS:
- a collection of gases held together by inertia
- a group of planets revolving around a single star
- a collection of stars and gases with the Sun as its center
- a group of stars, dust, and planets held together by gravity
A: a group of stars, dust, and planets held together by gravity

The flower petals of a hydrangea plant change color as the acidity of the soil changes. The color changes are directly related to which factor? OPTIONS:
- gravitropism
- photosynthesis
- geographic location
- environmental conditions
A: environmental conditions

Which gas makes up the greatest percentage of Earth's atmosphere? OPTIONS:
- argon
- nitrogen
- nitrous oxide
- carbon dioxide
A: nitrogen

What advantage do sea stars gain from having radial symmetry? OPTIONS:
- They reproduce at a faster rate.
- They digest food more efficiently.
- They move quickly along the ground.
- They sense predators and potential food from all directions.
A:
They sense predators and potential food from all directions.