15. Which sentence CAN'T be used with 'must'?
a. I... train a lot to win the game. It's important for me.
b. The rules say that you... turn on the light when cycling at night.
c. Athletes... wear a specific outfit for gymnastics, but if they want, they can wear a gymnastics suit.
Answers & Comments
c. Athletes must wear a specific outfit for gymnastics, but if they want, they can wear a gymnastics suit.
In this sentence, the use of "must" implies a requirement or obligation, but the phrase "if they want" suggests that wearing a gymnastics suit is optional. The use of "must" contradicts the idea of optional choice.