英语语法名词性从句知识点：whether 和if引导名词性从句
<p> 【导语】英语语法让很多学生都头疼，因为复杂难懂的句式和词组有时难以记忆。英语网为大家整理了英语语法大全，希望对同学们的英语语法学习有所帮助。更多内容尽在英语网。</p><p> 两者均可用于及物动词后引导宾语从句，表示是否，常可互换。但除此(用于动词后引导宾语从句)之外，在其他情况下表示是否时，通常要用 <span word="whether">whether</span> 而不用 <span word="if">if</span>，如用于引导主语从句、表语从句、同位语从句、让步状语从句、与<span word="or">or</span>连用分别引导两个分句等，或用于不定式前、用于介词后、直接与 <span word="or">or</span> <span word="not">not</span> 连用等等。如：</p><p> <span word="Ask">Ask</span> <span word="him">him</span> <span word="whether">whether</span> [<span word="if">if</span>] <span word="he">he</span> <span word="can">can</span> <span word="come">come</span>. 问他能不能来。</p><p> <span word="The">The</span> <span word="question">question</span> <span word="is">is</span> <span word="whether">whether</span> <span word="he">he</span> <span word="can">can</span> <span word="do">do</span> <span word="it">it</span>. 问题是他能不能做。</p><p> <span word="Answer">Answer</span> <span word="my">my</span> <span word="question">question</span> <span word="whether">whether</span> <span word="you">you</span> <span word="can">can</span> <span word="help">help</span> <span word="him">him</span>. 回答我你是否能帮助他。</p><p> <span word="It">It</span> <span word="depends">depends</span> <span word="on">on</span> <span word="whether">whether</span> <span word="the">the</span> <span word="letter">letter</span> <span word="arrives">arrives</span> <span word="in">in</span> <span word="time">time</span>. 这取决于信是否来得及时。</p><p> 注：在某些动词后(如 <span word="discuss">discuss</span> 等) 通常只用 <span word="whether">whether</span>。如：</p><p> <span word="We">We</span> <span word="discussed">discussed</span> <span word="whether">whether</span> <span word="we">we</span> <span word="should">should</span> <span word="hold">hold</span> <span word="a">a</span> <span word="meeting">meeting</span>. 我们讨论了是否要开一个会。</p>
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