I'm not sure about that.我想不大可行吧。
I wouldn't say that.我不赞成。
I 'm not sure that the case.我不确定是否是那样。
Why not?为什么不?
It may not be that simple.问题可能没那么简单。
I don't often use them.我很少使用。
I Wouldn't really know.我不知道。
I 'm not really sure.我不大不确定。
I wouldn't know anything about that.我不知道。
There is nothing wrong with that.那个没有什么不好。