They are inexpensive. They help keep the air clean. They can take millions of years to form. They are used because they are easily removed from the ground.
I gave my students this multiple choice question: Which of these statements about nonrenewable resources is true?

Only one answer is correct among these 4 choices:
- They are inexpensive.
- They help keep the air clean.
- They can take millions of years to form.
- They are used because they are easily removed from the ground.

Could you tell me which one is correct?

They can take millions of years to form.