什么时候用need do 什么时候用need to do？,比如need buy 与need to buy l need to buy a first.什么意思。

need to buy\u7528\u7684\u4ec0\u4e48\u53e5\u578b

need to buy\u7528\u7684\u4ec0\u4e48\u53e5\u578b
need \u662f\u5b9e\u4e49\u52a8\u8bcd\uff0c\u4e14\u662f\u53ca\u7269\u52a8\u8bcd\uff0c\u8868\u9700\u8981\u3002
to buy \u662f\u52a8\u8bcd\u4e0d\u5b9a\u5f0f\u3002
need to buy \u662f\u52a8\u5bbe\u7ed3\u6784\uff0c\u52a8\u8bcd\u4e0d\u5b9a\u5f0f to buy\u4f5cneed\u7684\u5bbe\u8bed\uff0c
\u5426\u5b9a\u5f0f\u662f don't need to do / doesn't need to do.

\u6211\u9700\u8981duy\u7b2c\u4e00.

need do中，need是情态动词。need to do中，need是行为动词。但是需要指出的是，情态动词need通常不会在肯定句中出现，多是在否定句needn't do或是疑问句，need sb do中出现。因为肯定句中出现的应该都是need to do的形式。而且need to do可以在所有种类的句型中出现

肯定句时：
当主语是人的时候：need to do 如 I need to have a rest. 我需要休息
当主语是物的时候：need doing 如 The clothes need washing. 这些衣服需要洗
只有在疑问或否定的时候，need 作为情态动词，才可接动词原形。如 Need you sit down?
He needn't sit down. 这就是所谓的 need do

希望我的回答能够帮到你，望采纳！
祝你学习进步，天天快乐。O(∩_∩)O

need to do sth 需要做某事
这里need 是实义动词，后面接不定式结构。

need 还可以作情态动词，但是要用于否定句或者疑问句中，比如：
You needn't go home now.

祝你学习进步，更上一层楼！(*^__^*)

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