need可做情态动词,但通常以否定形式出现Must I wash the dishes?否定回答：No,you need't.只是must开头的时候才会吗?can should呢?1.He does not need________(do) too much homework.2.You need to eat more vegetbables.(改为否定句）

问句的意思是：我必须要洗碗吗？
回答显得合理一点的话就要用needn't，意为不必，也就是不是一定要洗。如果用mustn't,意为禁止，常用于标语中，用在这种回答不合适。
而can should 开头的问句一般就用它们回答。
例如：can i ask you some questions?
yse,you can.
should we go for a walk ?
yes,we should.
1.to do
2.You needn't(don't need to) eat more vegetables


我之前也老纠结这个 不过熟悉了就好了。学习进步。

Must I wash the dishes?否定回答：No,you need't.对
Can I...Yes,you can.No,you can't
Should I．．．?　　　　Yes,　　you　　should．　　No,　　you　　shouldn＇t．
1.He does not need_to　　do_______(do) too much homework.　　　　因为前面用助动词does了,所以这里need是实义动词,要用to　 do
2.You need to eat more vegetbables.(改为否定句）　
You　 don＇t　 need　 to　 eat　 more　 vegetables．　
因为need　后面没有用动词原形,而加了to　 do,所以这里是实义动词