Fossils of a shellfish was found high on the top of a mountain. Which BEST explains how this is possible?

Responses
A the shellfish were dropped there by flying birdsthe shellfish were dropped there by flying birds
B the rocks of the mountain were once under water
the rocks of the mountain were once under water
C the shellfish were brought there by humans millions of years agothe shellfish were brought there by humans millions of years ago
D the rocks of the mountain were formed from an underwater volcano

B the rocks of the mountain were once under water