antagonist

在故事中，年轻的侦探必须智胜他的主要对手。

In the story, the young detective must outsmart his main ___antagonist.

这种药物作为拮抗剂，可以中和毒素的作用。

This medication works as an ___antagonist to neutralize the toxin's effects.

当屈膝时，股四头肌作为腘绳肌的拮抗肌发挥作用。

The quadriceps acts as the ___antagonist to the hamstrings during knee flexion.