as引导状语从句的常见用法如下:1. 引导时间状语从句，表示“在……时”=when/while，比如:I saw him as I was getting off the bus. 我下公共汽车时看见了他。
Ifit has to hire a caregiver for every two children, it can’t really achieve any economics of scale on labor to save money when other expens
My mother was cooking in the kitchen while1 I was doing my school assignments. As soon as2I finished my homework， I went to get some water to drink. Then the doorbell rang. However， my sister unlocked the door before3I could open it. We were surprised the moment4we saw her because5 her clothes and face were terribly dirty.She looked much poorer than⑥we expected. Since⑦ we didn't know what had happened to her， we stood there and waited for my sister's story.We wouldn't leave unless⑧ my sister told us all about it.After⑨my sister got changed， she told us that she fell into a ditch when⑩ she walked on a path on her way to my uncle's home in the countryside. She couldn't get out of the ditch.Although⑪she cried for help， no one could hear her. She tried to climb out of it， but， however⑫hard she tried， she failed to escape from it.As⑬time went by， she got worried. After several vain attempts she had to stand where⑭ she was and waited until⑮ a boy student passed by and gave her a hand. The boy reached her a long rope and told her to climb with the rope.She did as⑯the boy told， so⑰ she came out.My sister also warned us to be careful when walking⑱ on a path even_though/if⑲ we are in a great hurry.That's true. We should mind our step so_that⑳ we can ensure our safety.
