need.
1.情态动词.
常用于否定句、疑问句和条件句.没有人称和时态的变化,后接动词原形.
否定式直接加not,疑问式将need提前.
You needn't be told twice about one single thing.
同一件事没有必要对你说两次.
2.实意动词.
有人称和数的变化,后面接带to的不定式,其否定式、疑问式都要通过助动词do构成.
I need to go to Beijing this Sunday to attend a meeting.
上面很详细了.我们老师讲过了.