the birds living in the area of the bones the weather conditions in the area of the bones the kinds of trees living in the area of the bones the index fossils in the area of the bones
I gave my students this multiple choice question: A scientist finds the bones of a dinosaur. What could help the scientist determine the approximate age of the dinosaur bones?

Only one answer is correct among these 4 choices:
- the birds living in the area of the bones
- the weather conditions in the area of the bones
- the kinds of trees living in the area of the bones
- the index fossils in the area of the bones

Could you tell me which one is correct?

the index fossils in the area of the bones