I know it's difficult to do that.

I know it's difficult to do that. I know that it's very difficult to stop smoking but you must Is difficult to forget the past~But i know it's hard but i g i know that it is very difficult to stop smoking ,but you __ i know that it's hard to understand I know that it's easy for U to go. I found that it was difficult to do the math probiem.I found Winter is dangerous because it’s so difficult to know what i It's difficult to get to know a reserved people 1.I found that it was difficult to do the math problem. I found that it was difficult to do the math problem.（改为简单句） i found that it was difficult to do the math problem改简单句