He hurried home，looking behind as he went.

　　他匆忙回家去，一边走一边回头望。

　　As time went on，it's getting warmer and warmer.

　　随着时间的推移，天越来越暖和了。

　　2．till和until

　　在肯定句中主句谓语动词应是延续性的，而在否定句中主句谓语动词应是非延续性的；till不可位于句首，而until则可以。

　　You may stay here till/until the rain stops.

　　你可以待在这里直到雨停。

　　I won't see him till/until his anger has cooled down.

　　等他怒气消了，我再去看他。

　　Until you told me，I had no idea of it.

　　直到你告诉我，我才知道这件事。

　　[名师点津]　

　　not until置于句首时主句要用部分倒装。

　　Not until nine o'clock yesterday evening did we finish the work.

　　直到昨晚九点，我们才完成这项工作。

　　3．before和since

　　(1)before本意为"在......之前"，还可引申为"还未......就......，不到......就......；趁......；还没来得及......就......"。before引导时间状语从句的常用句型：

　　①It was＋时间段＋before从句(一般过去时)过了多久才......

　　②It will be ＋时间段＋before从句(一般现在时)要过多久才......

　　He had put the broken vase away before his mother came back.

　　他趁妈妈还没回来就把打碎的花瓶收拾好了。

　　It was some time before we realized the truth.

　　过了一段时间我们才了解了真相。

　　It will be half a year before I come back.

　　半年之后我才回来。

(2)since意为"自从......以来"，主句用完成时。since引导的从句如果用