Which feature of the ocean floor includes its deepest parts? trench estuary mid-ocean ridge continental slope

the deepest part of the ocean floor represents ocean trenches.

trench  

Oceanic trenches are deepest parts of the ocean.These are the depressions in the ocean. These are formed by the phenomena of plate tectonics, when old ocean crust from one tectonic plate is pushed below the another plate. This results in formation of underwater mountains, generation of earthquakes and volcanoes on the sea and on land.

the answer would be d