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