be going to / will
        
        用于条件句时， be going to　表将来
        　 will　表意愿
        If you are going to make a journey, you’d better get ready for it as soon as possible.
        Now if you will take off your clothes, we will fit the new clothes on you in front of the mirror.
        
        11.6 be to和be going to
        
         be to 表示客观安排或受人指示而做某事。
         be going to 表示主观的打算或计划。
        　I am to play football tomorrow afternoon. (客观安排)
        　I’m going to play football tomorrow afternoon. (主观安排)