B or d.... hope this helps:)
Answer:
It is called mimicry when a living thing copies the appearance of another living thing as a means of protection.
Explanation:
Mimicry is used primarily by living things as a means for protection and to decrease the chances of the living thing being killed. For example, a frog that is prey to a toad could have bright colors (bright color frogs are often poisonous) that don't mean anything to the frog and it's species, but to the toad, the frog is poisonous and should not be eaten, so the toad does not eat the frog because it is brightly colored.
Without mimicry, the frog would have been eaten because it wouldn't have had looked like a poisonous frog, or something that the toad would avoid.
Shells are considered biotic because they come from living things. Biotic describes something living or use to be living such as plants and animals. So shells are considered biotic because they come from a living organism.
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Hope that helped:)
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