We must remember that a trace fossil is as its name indicates, the traces of an animal rather than parts of an animal or the animal itself, In the list, we can discard options C and D because are parts of an animal, meanwhile, we have the cast of a shell which is the imprint of a shell and fossilized dung which is a coprolite, in both cases, we have an animal trace, not the animal itself, now if we are very strict the only one that would be an imprint is the shell, option B.
