The question is too difficult I __ (not understand) it

The question is too difficult I __ (not understand) it
The question is too difficult I __ (not understand) it

The question is too difficult I __ (not understand) it
是必须用这俩词 还是有这意思啊 如果是括号里的意思可以是to understand 如果必须用括号里的就是can not understand

can't understand

can't understand
不过我觉得好像这个句子怪怪的。。。

The question is too difficult I _can't understand_ (not understand) it