one plate is sliding past another. one plate is being forced beneath another. two plates are colliding into each other. two plates are pulling apart from each other.
I gave my students this multiple choice question: The Mariana Trench is the deepest ocean trench on Earth. This trench occurs at a plate boundary where

Only one answer is correct among these 4 choices:
- one plate is sliding past another.
- one plate is being forced beneath another.
- two plates are colliding into each other.
- two plates are pulling apart from each other.

Could you tell me which one is correct?

one plate is being forced beneath another.