Unit 10 单元语法知识点讲解if引导的条件句+练习 2023-2024学年人教版八年级英语上册

U10语法知识点 If 引导的条件句 一、种类： 分为真实性条件状语从句和非真实条件句。 If you do ,you’ll have a great time. （真实性条件状语从句，就是可以在现实生活中发生的。） If I was a bird, I could fly.（非真实性条件状语从句，就是在现实生活中不能发生的。） 二．定义： If 意为“如果”，引导条件状语 从句，表示假如从句的动作发 生，主句的动作就(不)会发生。 If you do, the teachers won't let you in. 三．从句位置： 从句位置灵活，可放在主句之 前，但要用逗号与主句隔开；也 可放在主句之后。 Mary will watch a movie with me if she is free on Sunday. If she is free on Sunday, Mary will watch a movie with me 四．三种用法 if从句一般有三种用法 1、主将从现 （主句为一般将来时,从句为一般现在时）； eg:If it rains(从句) ,I will stay at home（主句）. =I will stay at home if it rains. 2、主句含有情态动词 （must、may、can etc.）从句为一般现在时； eg:If you drive too fast ,you may have an accident. =You may have an accident if you drive too fast 3、主句为祈使句,从句要用一般现在时态； eg:Don't play computer games if you don't finish your homework. 备注： 1、If 于句首时中间用逗号隔开,主句后不用逗号. 2、if 可用unless(除非...) 替换.unless= if...not... 例如： We will be late if we do not hurry. 等同于 We will be late unless we hurry. 3、注意虚拟语气 主句和从句都为一般过去式 eg:If I was a bird ,I could fly.（事实我不可能是鸟） 五：与其他句式之间的转换 (1) 借助“祈使句+and / or+ 一般将来时的句子”这一句型来转换。and在句意上表示顺承关系, or表示转折关系。如: If you get up early, you'll get there on time. = Get up early, and you'll get there on time. = Get up early, or you won't get there on time. 早点起床, 你就会准时到那里。 (2) 借助介词without或with来转换条件状语从句。如: If there is no water, fish will die. = Fish will die without water.如果没有水, 鱼就会死。 If you help me, I'll finish the work soon. = With your help, I'll finish the work soon. 如果你帮助我, 我就会快点完成工作。 (3) if … not 导的条件状语从句, 可以借助连词unless来改写。如 You will be late if you don't go there by bus. = You will be late unless you go there by bus. 如果你不乘公共汽车你就会迟到。 六．if相关词组 if you want/like 如果你愿意的话 You can come and stay with us if you want. if so如果是的话 Are you planning to return to work, and if so, who is going to look after the baby? if not如果不是的话 as anyone dealt with the technical problems? And if not, why not? if necessary/if possible 如果必要/可能的话 We are ready to fight for our rights if necessary. I should like to be back here by 10:30 if possible. even if即使