supposing she doesn't come,what shall we do?这里suppose为什么用ing形式

很高兴为你解答.
保证正确率~!
【解析】：
suppose本来是动词,supposing本来是现在分词,但它们有可用作【连词】,引导条件状语从句,其意为“假若”“如果”等；此时主句通常为疑问句.如：
Suppose [Supposing] (that) we miss the train,what shall we do?
假如我们误了火车,我们将怎么办?
【注意】：
suppose用作连词引导条件状语从句时,它必须置于主句之前,但supposing用作连词引导条件状语从句时,则可置于主句之前,也可以置于主句之后.如：
We'd love to come and see you on Saturday,supposing I don't have to work that day.
我想星期六来看你,假若那天我不上班的话
祝开心~!意思是放在句首时，加不加ing都可以是吧是的。