the total mass of the rock the rate at which the rock formed the types of fossils that the rock contains the amount of time passed since the rock formed
I gave my students this multiple choice question: The radioactive isotope content of a rock can be used to identify which property of the rock?

Only one answer is correct among these 4 choices:
- the total mass of the rock
- the rate at which the rock formed
- the types of fossils that the rock contains
- the amount of time passed since the rock formed

Could you tell me which one is correct?

the amount of time passed since the rock formed