Actually the correct answer is,Trench.
<em><u>Definition of trench:</u></em>
<em><u>A long, narrow ditch,Dig a trench or trenches in (the ground).</u></em>
As seen the meaning of trench now you know that is the correct answer.
Replace the sentence from "The Grand Canyon,as seen here,can be compared to a(n)_______under the earth's ocean."To"<u>The Grand Canyon,as seen here,can be compared to a(n) trench(narrow ditch) under the earth's ocean.</u>So the correct answer is A trench.
Ps,Bri <3
Plz give brainlyiest :)