could might must 后面要加动词原形
当是形容词,名词或者动词ing形式（动名词）的时候就要在could might must 后面先加be
Is the strange creature an alien (could)
The strange creature could be an alien.
Is she looking for something (must )
She must be looking for something.
这里是动名词,要先加be
Dose gesture mean "hello"?(might)
The gesture might mean "hello".
这里mean就是动词原形,可以直接加
Will our team win the match (could)
Our team coule win the match.
Is the woman with a camera coming to our school (most
The woman with a camera must be coming to our school.