Question is in the image below.

It's the last one

Explanation:

The grand canyon was formed by erosion of water. That is the only option with erosion of water for the grand canyon

currents is the correct answer.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)