The correct option is C. Because it is a hard body part
Explanation:
Evolutionary studies have shown that those organisms are most likely to be preserved in the earth's surface which are hard and have the ability to decay over a long period of time. As evidences have shown the softer parts of a body do not get preserved and they decay earlier than the hard parts.
As the clam shells are hard and do not contain any soft body parts, hence they are most likely to be preserved.
