hold one's tongue 保持沉默
I.O.U = I owe you 我欠你；借据
in hot water 遇到麻烦
in the hole 遇到经济困难
in the long run 从长远来看;终究
in the soap 遇到麻烦
keep one's head 镇定
keep one's shirt on 不动手打架
keep punching 继续努力
kick off 开始干某事
knock it off 别再讲下去了
let the cat out of the bag 泄漏秘密
let nature take its course 顺其自然
Knock on wood. 说话禁忌；赶紧讨个吉利.
kill two birds with one stone 一石二鸟