I really can't understand you ________ (treat) her like that.

I really can't understand you ________ (treat) her like that.
I really can't understand you ________ (treat) her like that.

I really can't understand you ________ (treat) her like that.
treating,这里是ing形式表主动,我真的不能理解你那样对她.这个treating修饰you,因为是主动的对待,所以用ing形式.

treated