助动词do 系动词BE的用法

do是修饰动词的，名词、形容词等其它词前用BE动词。

be动词后可以跟各式各样的表语：
形容词、名词、副词、介词短语、代词、不定式、数词、现在分词、过去分词、从句、词组等都可以搭配使用。
可构成进行时态，被动语态，复合谓语。

do可构成疑问句、否定句、用于强调或代表前面动词以避免重复。

do的用法
do的基本含义是做，进行，它的同义词为perform, accomplish. 一般讲do 的宾语并不十分具体，比如“事情”。而make 的基本含义是“制造，作出”，它的同义词为form, forge, fabricate, manufacture. 。
I don't know what to do.
我不知道干什么好。
What shall I do?
我怎么办呢？
to do one's best
作最大的努力。
to do one good (harm)
对某人有好处(害处)
be 的用法
Traditional grammar requires the nominative form of the pronoun in the predicate of the verb be: It is I (not me); That must be they (not them), and so forth. Even literate speakers of Modern English have found the rule difficult to conform to, but the stigmatization of It is me is by now so deeply lodged among the canons of correctness that there is little likelihood that the construction will ever be entirely acceptable in formal writing. Adherence to the traditional rule in informa