hold one's tongue 保持沉默

I.O.U = I owe you 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