問題詳情：
改錯：You need have studied that late last night. It was harmful to your health.
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【回答】
need→needn't 由後面的句子可知，前一句句意為“昨天晚上你不必學到那麼晚”，因此應用need的否定形式。needn't have done “本不必做某事(而實際上做了)”。
知識點：虛擬語氣
題型：短文改錯
