Jupiter is the largest planet in the solar system. It rotates on its axis once about every 10 hours. What time period on Earth would be 10 hours long if Earth rotated on its axis once every 10 hours? OPTIONS:
- a day
- a week
- a month
- a year
A: a day

Why do planets stay in orbit around the Sun? OPTIONS:
- attraction of gravity
- effect of inertia
- frictional force
- rotational force
A: attraction of gravity

Which action is the best method to separate a mixture of salt and water? OPTIONS:
- using a magnet to extract the salt
- adding a colored dye to the mixture
- pouring the mixture through a filter
- boiling the mixture until the water evaporates
A: boiling the mixture until the water evaporates

Which human activity has most negatively affected air quality? OPTIONS:
- burning coal
- growing crops
- using solar energy cells
- constructing nuclear power plants
A:
burning coal