They are composed mostly of iron. They are composed mostly of ice. They regularly revolve near the Sun. They regularly replenish water on Earth.
I gave my students this multiple choice question: Which property is thought to characterize objects in the Oort Cloud?

Only one answer is correct among these 4 choices:
- They are composed mostly of iron.
- They are composed mostly of ice.
- They regularly revolve near the Sun.
- They regularly replenish water on Earth.

Could you tell me which one is correct?

They are composed mostly of ice.