Trenches in the ocean are

A. close to the shore

B. on the continental shelf

C. the deepest part of the ocean.

D. Part of the intertidal zone.

C. the deepest part of the ocean

Explanation:

Take for example the Mariana Trench, the deepest trench in the ocean.

A and D are the same thing almost.

B is the part of the continent underwater, but its shallow water.