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1、if从句（if条件状语从句）He will play the solo.If he beats you , he will play the solo.If he beats you“If he beats you”有自己的主谓结构，是一个句子，但在If he beats you , he will play the solo.的整体结构中，“If he beats you”只是充当一个状语的成份，是一个状语从句，“he will play the solo.”是主句（主句是表达主要意思的句子）。一、if 从句 + 祈使句(1)if 从句的谓语动词若为be动词，其肯定形式为am/is/are,
2、 否定形式为am not/is not(isnt)/are not(arent)。If I am (be) free, go shopping with me.If I am not (be not) busy, take me around your school.If the photo is (be) good, print it.If the apple isnt (be not) good, change another one.If you are (be) happy, clap your hands.If they arent (be not) free, dont call
3、them.(2)if 从句的谓语动词若为行为动词，其形式遵循行为动词一般现在时变化规律，即：if 从句的主语为第一人称单复数、第二人称单复数以及第三人称复数时，肯定形式为V原形，否定形式为dont + V原形；if 从句的主语为第三人称单数时，肯定形式为动词三单形式，否定形式为doesnt + V原形。If you want (want) to listen to the popular songs, turn on the computer.If they dont like (not like) the TV programme, turn off the TV.If he comes (
4、come) here, tell me.If it doesnt rain (not rain), go out for a walk.二、if 从句 + 其他形式的句子，一般采用“主将从现”结构，即主句用一般将来时，if从句用一般现在时。如：If I finish my homework, I will watch TV.If you dont hurry up, well be late.If he comes, they will go together.If she doesnt study hard, her parents will punish her.if 从句 + 其他形式的句子，if 从句表示将来的条件，一般情况下采用一般现在时，即使出现将来的时间词，if 从句也采用一般现在时。如:If you dont do it, I will do it myself.If Tony comes here, I will go.If it rains tomorrow, we will stay at home.If she doesnt finish her homework tomorrow, the teacher will be very angry.