What we have to do is to put the glass down ,rest for a while before hoding it up.
这时一个含有主语从句的复合句结构,里面没有补足语。
What we have to do 是主语从句。主语从句的主语是 we,它的谓语是 have to do, what充当do的宾语
复合句的谓语是 is to put the glass down (这是连系动词 is+ 表语不定式短语构成谓语。)
rest for a while (这也是谓语一部分,它是动词短语(意思为休息一会)。前面省略了 is to)
before holding it up 作时间状语(因为before是介词,后面要用动名词动ing作其的宾语)。
=before we hold it up. 可以用时间状语从句替换上面的介词短语 before holding it up。)
主句就是整个句子------What we have to do is to put the glass down, rest for a while
主语从句 谓语(系表结构作谓语)
before holding it up.
时间状语