11.6 be to和be going to

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)