Flat Earth?

From Twitter:

A. You think Earth is flat?
1. B. Yes. __ it isn’t.
2. A. I can show you the __.
3. B. What’s your __?
A. Ever seen a lunar eclipse?
B. Sure.
A. Earth’s shadow is curved on the moon.
B. That’s the moon’s curve!
A. Ug. So–fly to 13,624 ft, or higher!
B. Oh.

a. proof
b. evidence
c. prove

Answers and Explanation:
1. c., prove (a verb)
2. a., proof or b., evidence (both nouns)
3. a., proof or b., evidence (both nouns)