lay
1.lay（放置）是及物动词，它的过去式和过去分词都是laid。lie（躺）是不及物动词，它的过去式是lay，过去分词是lain。注意lay的现在式和lie的过去式完全相同。把laid用作不及物动词是英美人常有的错误。注意下面各句里的lie，lay，lain和laid：
- The books still lie where I laid them a month ago.
- The books still lay where I had laid them a month before.
- The books have lain here ever since they were laid here.
- Let us lay the books here.
2.lain比较少用，上面第三句里的lain改作been lying普通些。
