21．______ no use discussing it with me. You’d better consult the teacher.                   

       A．That's                  B．You're                 C． It's                    D．There's

22．Set the alarm for an earlier time. _______ be late again tomorrow!                              

       A．Not be sure to      B．Don’t be sure to   C．Be sure not to      D．Be sure don’t

23．Now, ______ were we? Oh yes, we were talking about John.                                

       A．how                    B．where                 C．what                   D．who