be动词后能跟介词么?(be for?有这种用法么?)

e构成的句子结构：主系表,也就是说能够充当表语的都能放在be的后面.
表语可以是：
1.名词或代词He is a teacher.
2.副词 Time is up.
3.形容词He is tall.
4.现在分词The argument is convincing.
5.过去分词,He is exhausted.
6.数词 I am eleven.介词 Are you up yet?(你起床了吗) It is up to you(你说了算/ 你自已决定)
7.不定式短语 He is to Beijing.
8.从句 The truth is that he is cheated.

be 后面加表语或表语短语
如 I am from China

当然可以
be for sth 赞成/支持......; 是为了......

be动词后能直接跟prep