i really can't understand ___her like that.A you treatB you to treatC why treatD you treating选D 为什么

i really can't understand ___her like that.A you treatB you to treatC why treatD you treating选D 为什么
i really can't understand ___her like that.
A you treat
B you to treat
C why treat
D you treating
选D 为什么

i really can't understand ___her like that.A you treatB you to treatC why treatD you treating选D 为什么
D
AC缺少成分,应该为 why you treat.

是动名词 动词的doing形式做名词形式 再加上your做逻辑主语

you 是understand的宾语，treating her like that是一个现在分词引导的从句！