glaciers carried the fossils up the mountains the Rocky Mountains and the Swiss Alps are both volcanic in origin clams once lived in mountains, but have since evolved into sea-dwelling creatures the layers of rocks in which the fossils were found are from the same geologic age
I gave my students this multiple choice question: An unusual type of fossil clam is found in rock layers high in the Swiss Alps. The same type of fossil clam is also found in the Rocky Mountains of North America. From this, scientists conclude that

Only one answer is correct among these 4 choices:
- glaciers carried the fossils up the mountains
- the Rocky Mountains and the Swiss Alps are both volcanic in origin
- clams once lived in mountains, but have since evolved into sea-dwelling creatures
- the layers of rocks in which the fossils were found are from the same geologic age

Could you tell me which one is correct?

the layers of rocks in which the fossils were found are from the same geologic age