Hot lava cools and forms new rock. Water vapor condenses to form a cloud. A seismic wave travels through the mantle. An ocean basin forms between two continents.
I gave my students this multiple choice question: Which of the following processes usually takes the longest amount of time?

Only one answer is correct among these 4 choices:
- Hot lava cools and forms new rock.
- Water vapor condenses to form a cloud.
- A seismic wave travels through the mantle.
- An ocean basin forms between two continents.

Could you tell me which one is correct?

An ocean basin forms between two continents.