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 am hesitating between 4 options to answer the following question, which option should I choose?
Question: Which of these statements about nonrenewable resources is true?
Possibilities:
- 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.

They can take millions of years to form.