need 不必做和本不该做
<p> <span word="didn">didn</span>’<span word="t">t</span> <span word="need">need</span> <span word="to">to</span> <span word="do">do</span>表示： 过去不必做某事, 事实上也没做。.</p><p> <span word="needn">needn</span>’<span word="t">t</span> <span word="have">have</span> <span word="done">done</span>表示： 过去不必做某事, 但事实上做了。</p><p> <span word="John">John</span> <span word="went">went</span> <span word="to">to</span> <span word="the">the</span> <span word="station">station</span> <span word="with">with</span> <span word="the">the</span> <span word="car">car</span> <span word="to">to</span> <span word="meet">meet</span> <span word="Mary">Mary</span>, <span word="so">so</span> <span word="she">she</span> <span word="didn">didn</span>’<span word="t">t</span> <span word="need">need</span> <span word="to">to</span> <span word="walk">walk</span> <span word="back">back</span> <span word="home">home</span>. 约翰开车去车站接玛丽，所以她不必步行回家了。</p><p> <span word="John">John</span> <span word="went">went</span> <span word="to">to</span> <span word="the">the</span> <span word="station">station</span> <span word="with">with</span> <span word="the">the</span> <span word="car">car</span> <span word="to">to</span> <span word="meet">meet</span> <span word="Mary">Mary</span>, <span word="so">so</span> <span word="she">she</span> <span word="needn">needn</span>’<span word="t">t</span> <span word="have">have</span> <span word="walked">walked</span> <span word="back">back</span> <span word="home">home</span>. 约翰开车去车站接玛丽，所以她本不必步行回家了。 (<span word="Mary">Mary</span>步行回家，没有遇上<span word="John">John</span>的车。)</p><p>典型例题</p><p> <span word="There">There</span> <span word="was">was</span> <span word="plenty">plenty</span> <span word="of">of</span> <span word="time">time</span>. <span word="She">She</span> ___. </p><p><span word="A">A</span>. <span word="mustn">mustn</span>’<span word="t">t</span> <span word="have">have</span> <span word="hurried">hurried</span> <span word="B">B</span>. <span word="couldn">couldn</span>’<span word="t">t</span> <span word="have">have</span> <span word="hurried">hurried</span> <span word="C">C</span>. <span word="must">must</span> <span word="not">not</span> <span word="hurry">hurry</span> <span word="D">D</span>. <span word="needn">needn</span>’<span word="t">t</span> <span word="have">have</span> <span word="hurried">hurried</span></p><p> 答案<span word="D">D</span>。<span word="needn">needn</span>’<span word="t">t</span> <span word="have">have</span> <span word="done">done</span>. 意为本不必，即已经做了某事，而时实际上不必要。</p><p> <span word="Mustn">Mustn</span>’<span word="t">t</span> <span word="have">have</span> <span word="done">done</span> 用法不正确，对过去发生的事情进行否定性推断应为<span word="couldn">couldn</span>’<span word="t">t</span> <span word="have">have</span> <span word="done">done</span>, 不可能已经。 <span word="must">must</span> <span word="not">not</span> <span word="do">do</span> 不可以（用于一般现在时）。</p></p>
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