The answer would be A) TRUE because that's what the word means, flex is used to move muscles and move around and bility is short for ability where its our capability to move in motion.
The answer is force because Force is needed to change the direction of a moving mass.
If you sense that a friend is showing signs, id suggest asking the friend small questions, not BIG OBVIOUS ONES, that will eventually lead up to your answer, OR you could do some investigating and talk to some of the friends close ones, asking them if they know anything. hope this helps! if you'd like i could help you further