I will come back as soon as I [possibly] can .

possibly在这里作状语成分,其实分开看就是I possibly can.用possibly是因为有can,这句话其实可以说成I will come back as soon as possible.或者I will come back as soon as I can.不用把两个混在一起.这句话就是陈述句了,还要怎么改呢?