"快"的反义词是"慢"。

The ___opposite of "fast" is "slow."

我父亲是一个非常冷静的人，但我母亲正好相反。

My father is a very calm person, but my mother is just the ___opposite.

她结果与每个人预期的完全相反。

She turned out to be the exact ___opposite of what everyone expected.