flat
protuberant
full
indented
Answer is Wrong!
Answer is Right!
The correct answer is A. flat.
A convex surface is curved outward, like the outside of a ball. A flat surface is not curved at all. A protuberant surface is curved outward, like a bump. A full surface is completely covered, like a balloon that is filled to the top.
An indented surface is curved inward, like the inside of a bowl.In conclusion, the antonym of convex is flat.