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