161 It's a good idea for sb to do sth 对…… 来说是个好主意

　　162 It's important to sb 对某人来说很重要 eg: It's important to me

　　163 It's time to do sth It's time for sth 到了该去做某事的时间

　　eg : It's time to have class It's time for class 该去上课了

　　164 join = take part in 参加

　　165 just now 刚才

　　166 keep +sb /sth +adj /介词短语 让什么保持什么样？

　　167 keep out 不让 …… 进入

　　168 keep sb adj 让……保持…… eg: I want to keep my mother happy keep healthy 保持健康

　　169 key to +名词 表示：某物的钥匙或某题的答案

　　170 key to… anser to … key 可以是答题或钥匙