一、时间状语从句

　　as/when/while

　　1._________I was walking down the street，I noticed a police car in front of No.37.

　　When/while/As=During the time that (时间段)

　　2._________ Mary was writing a letter, the children were playing outside.

　　While=At the same time as 与……同时

　　3.The volume varies _________ the temperature increases.

　　as 体积随着温度增加而变化。

　　4.________ he stood up，he dropped the glass.

　　As/When=At the time that (时间点)

　　练习：

　　1. ____________I had done it，I knew I had made a mistake.

　　A. Direct B. Directly

　　C. Moment D. Constant

　　二、条件状语从句

　　if 好的条件，可用 provided/providing/suppose/supposing(that)/ on condition that 替换

　　不好的条件可用 so/as long as替换

　　如：If/Provided(that)it snows tomorrow, we shall play snowballs.

　　If/So long as it snows tomorrow, we shall delay our trip to the seaside.

　　练习：

　　1. We’ll visit Europe next year ______ we have enough money.

　　A. lest B. until C. unless D. provided

　　only if/if only

　　1.only if=only on condition that“只要，只有…”

　　如：Only if a teacher has given permission is a student allowed to enter this room.(主句例装)

　　只有得到教师的允许，学生才可以进这间屋。

　　2.If only“要是…就好了”(虚拟)

　　如：If only we had arrived in time，we would not have missed the train.

　　if/unless

　　unless=if…not (且语气较强)

　　如：You will make progress if you study hard.

　　比较：You will never make progress unless you study hard.

　　Unless he comes，we won’t be able to go.

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