1. 引导主、表、 同时，用whether不用if.
whether it is true remains a problem. (主语从句 )
The question is whether he will speak at the meeting. (表语从句 )
I am in doubt whether I should agree to the plan. (同位语从句)
2. 引导动词的宾语从句时, 既可以whether也可以if
Could you tell me us whether/if it rains in winter in Australia? (请告诉我冬天澳大利亚是否下雪?)
I don’t care if it doesn’t rain. (我不在乎是否下雨)
(注意1) 一般的说, whether引导的宾从, 强调正反两个方面的选择意义; 用if引导的宾从, 强调说话者希望得到正面意义或肯定意义的回答.
I asked the teacher if I could go. 我问了老师,我去行不行.(暗示我想去.)
I asked the teacher whetherI should go. 我问了老师,我是否也该去.(表示我去不去都可以.)
省心英语下载(注意2) 引导discuss的宾语从句，用whether不用ifWe discussed whether Mary could join us. (我们讨论了是否玛丽能同我们一起干)3. whether、 if常和 or not 分开使用, 有时也与or not连用(限whether)。I don’t know whether they will come or not. （我不知道他们来不来。）I don’t know whether or not they will come。 （我不知道他们来不来。）I don’t know if or not they will come。（×）4. 当whether引导的从句作介词的宾语或置于句首表示强调时，不能if与替换。whether可与不定式连用，if不可。Everything depends on whether we have enough money. (一切得靠我们是否有足够的钱来决定.) I wonder whether to go. 我不知道是否去.Whether he will come, I am not sure.我不能确定他是否来.5. 二者还可以引导状语从句, if引导的状语表示条件；whether引导的状语从句，表示让步，译为“不管、无论---”If we start at six, we’ll be there in time.（如果六点钟出发，我们会即时赶到那儿。）Whether you go or not, I will。（不管你去不去，我都去。）6. whether及if均可与or搭配, 构成“whether…or…”与“if…or…”意义为“或---- 或----”、“是----还是----”.He asked the teacher if/ whether I was going out or staying at home. （他问我是出去还是呆在家里.）题一： Do you know the speed ____ the car is running?A. at which B. which C. with which D. that题二： By n ine o’clock, all the Olympic torch bearers had reached the top of Mount Qomolangma, appeared a rare rainbow soon.A. which B. on which C. that D. above which题三： While driving through the city, she showed me the building ____ she once worked as a lift operator.A. among which B. which C. in which D. that题四： The sch ools themselves admit that not all children will be successful in the jobs ______ they are being trained.A. that B. for which C. which D. about which题五： Life is like a long race _____we compete with others to go beyond ourselves.A. why B. what C. that D. where答案题一： A详解：____ the car is running是定语从句，其先行词是the speed。定语从句与先行词可连接成the car is running at the speed。at …speed(以……的速度)为固定搭配。 题二： D详解：_____appeared a rare rainbow soon是定语从句，其先行词Mount Qomolangma，定语从句与先行词可连成above Mount Qomolangma appeared a rare rainbow soon。rainbow应在山峰的上空，故用介词above。题三： C详解：定语从句 she once worked as a lift operator可与先行词the building连成she once worked in the building as a lift operator。题四： B详解：定语从句______ they are being trained与先行词the jobs可连成they are being trained for the jobs。train sb. for sth.为固定搭配。题五： D详解：_____we compete with others to go beyond ourselves为定语从句，其先行词为race。因为从句缺少地点状语in the race, 故用where。