Plants began appearing on Earth. Dinosaurs became extinct on Earth. Earth's continents became separated. Earth's moon began orbiting.
I gave my students this multiple choice question: Which event must have occurred before coal and oil could be formed?

Only one answer is correct among these 4 choices:
- Plants began appearing on Earth.
- Dinosaurs became extinct on Earth.
- Earth's continents became separated.
- Earth's moon began orbiting.

Could you tell me which one is correct?

Plants began appearing on Earth.