need怎么区分它在句子中做的情态动词还是使役动词?

一、作情态动词
1．need作情态动词无人称或数的变化,后接动词原形,多用于否定句和疑问句中.
如：You needn't worry.你不必担心.
2．由need引出的一般疑问句,肯定回答常用must或have to;否定答语常用needn't.
如：
—Need I answer the question?我需要回答那个问题吗?
—Yes,you must./Yes,you have to.是的,你必须回答./是的,你得回答./No,you needn't.不,不必了.
3．由must引出的一般疑问句,肯定回答用must,否定答语用needn't或don't have to.
如：
—Must I do the work now?我必须现在干这个活吗?
—Yes,you must /have to.是的,你必须做./No,you needn't /don't have to.不,你现在不必做.
二、作行为动词/使役动词
need 作为行为动词有人称和数的变化,后面可接名词、代词、动名词及带to 的动词不定式；可用于肯定句、疑问句和否定句中,
如：
She needs help.她需要帮助.
I don't need to see the doctor.我不需要看病.
Do you need to go at once?你需要马上走吗?
—Yes,I do.是的,我得马上去.
—No,I don't.不,不用马上走.
整理了一下,