Question

why is a shell considered to be biotic?
because it is found in the biosphere
because it was alive
because it came from something living
because it is not living

Explanation:

Biotic factors are components of an ecosystem that are or were derived from living organisms. A shell itself is not alive, but it is secreted by a living organism (like a mollusk). The other options are incorrect: being in the biosphere doesn't make something biotic (abiotic things are also in the biosphere), the shell was never alive itself, and "not living" describes abiotic factors.

Answer:

because it came from something living