Oceans Are About Four Times as Deep as Mountains Are

Oceans are about four times as deep as mountains are high. At the bottom of the ocean are

A) towering mountains, deep valleys, and deep trenches near the continental borders.
B) thick layers of basaltic crust at midocean ridges that gradually thins near deep ocean trenches.
C) towering plutonic mountains created from volcanoes and fissures at oceanic ridge areas.
D) all of these