cancel(取消)/challenge(向. . .挑战)

7、cancel(取消)

The pros(赞成的意见) and cons(欺骗) cancel out(使平衡[抵消]).

正反两种意见抵消。

8、challenge(向. . .挑战)

Once students do not think what a teacher says is right, they challenge him.

一旦学生认为老师说得不对，他们就提出质疑。