a freshwater lake in the mountains marine fossils in a freshwater lake saltwater clams in the ocean a sandy beach next to the ocean
I gave my students this multiple choice question: Which of these provides the best evidence that an environmental change has occurred?

Only one answer is correct among these 4 choices:
- a freshwater lake in the mountains
- marine fossils in a freshwater lake
- saltwater clams in the ocean
- a sandy beach next to the ocean

Could you tell me which one is correct?

marine fossils in a freshwater lake