Hey there!
Antonym means the "the opposite meaning of a word"
Based on the definition we have above... Let's answer your question.
We can eliminate option D as one of your answers because destroy is a synonym of dismantle ❎
We can eliminate options B and C has nothing to do with it. ❎
This leaves us with option A as your answer because it is an opposite meaning of dismantle ✅
Answer: Option A. ✅
Good luck on your assignment and enjoy your day!
~LoveYourselfFirst:)