Biology

The correct answer is: D.Commensalism.

In this relationship:

1.Hermit crabs use the empty shells that snails have made and then abandoned. The hermit crabs benefit because the shells provide them with protection and a place to live.

2.The snails are not harmed by the hermit crabs using their old shells. Once the snails abandon their shells, they have no further involvement with them, and the shells are left empty for other creatures like hermit crabs to use.

This is a commensal relationship because the hermit crabs benefit from the shells, while the snails are unaffected (neither helped nor harmed).

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