有主语 +be +介词短语这种句型吗?

你说的是“主语+系动词+表语”的句型，这种句型用来描述主语的性质，状态，类属和身份。介词结构做表语时，通常就是指主语的状态的。He is in a low mood.
中间的系动词必不可少，起联系主语和表语的作用。系动词除了be动词以外，还有一些实义动词也可称当。

能做表语的成分有：
1.形容词及其结构
§The flowers are beautiful to look.
§This maths problem is hard to work out.§
2.介词结构
§My book is on the desk.§
3.个别副词(around, abroad,everywhere)
§My daughter is abroad.

4. 非谓语动词及其结构（含不定式，分词和动名词）
§My ideal is to be a successful pilot
.§His car is broken.§The film is exciting.
§5. 名词及其词组
§His father is a famous engineer

有啊。 She is in our classroom.
The pen is on the table .
介词短语可以作表语。 其实上面两句是主系表结构。

主系表结构 只要表语是介词短语的都是

有啊：
The book is on the table.
We will be at home by then.