Okay, I'm gonna put these answers in order (randomly):
Why does the Earth orbit the sun?
A. The Earth is moving and therefore must stay in motion.
B. The sun's gravitational pull keeps the Earth in a curved orbit.
C. The speed of the Earth's motion keeps it from crashing into the sun.
We can use the process of elimination.
Let's start with A.The Earth is moving and therefore must stay in motion.
The thing is, how does the earth move? Which kind of brings us back to to the original question, so it doesn't answer it.
C. The speed of the Earth's motion keeps it from crashing into the sun.
Again, how does the Earth move in the first place? And also how does the speed stop it from crashing into the sun? Lol
B. The sun's gravitational pull keeps the Earth in a curved orbit.
Here, we have an answer on how the Earth is moving in it's orbit. Gravity.
Therefore, I think the answer is B. The sun's gravitational pull keeps the Earth in a curved orbit.