YOU SAID:

I don’t know this is tough

INTO JAPANESE

私はこれが難しいことを知りません

BACK INTO ENGLISH

I do not know that this is difficult

INTO JAPANESE

これが難しいことはわかりません

BACK INTO ENGLISH

I don't know that it is difficult

INTO JAPANESE

難しいことはわかりません

BACK INTO ENGLISH

I do not understand the difficult thing

INTO JAPANESE

難しいことがわかりません

BACK INTO ENGLISH

I do not understand that it is difficult

INTO JAPANESE

難しいことがわかりません

BACK INTO ENGLISH

I do not understand that it is difficult