Question

What is plate tectonics?
a. The theory that Earth's surface does not change.
b. The theory that Earth's surface will eventually become hotter over time.
c. The theory that the thickness of Earth's crust will even out over time and become flat.
d. The theory that Earth's crust is composed of many plates that are moving slowly over time.

Answer 1

Plate tectonics is the theory that Earth's crust is composed of many plates that are moving slowly over time. 

Your answer is D. :)

Answer 2

What is plate tectonics?a. The theory that Earth's surface does not change.
b. The theory that Earth's surface will eventually become hotter over time.
c. The theory that the thickness of Earth's crust will even out over time and become flat.
d. The theory that Earth's crust is composed of many plates that are moving slowly over time.

This is the theory of plate tectonics :D