There be...doing 一定是进行时吗

Question

但是我觉得这个句型只是因为有两个动词，而一个句子中不能出现两个动词.......

Answer 1

必须是

be doing: 代表了正在干某事现在进行时
I'm doing my home work now

doing：动词ing形式做名词用
swimming is good for our health.
I like swimming
当动词be后所接的名词是单数可数名词或不可数名词时，be 应该取单数is；当其后所接的名词是复数的可数名词时，be用复数are。
例： There is/are sb doing…
There is a bird flying in the sky.
There are two boys swimming across the river.