题干
—Look!The man at the gate _____ be our headmaster．He is always standing there every morning．
—No，it_______ be him．He is holding a meeting in the office now．（ ）
A：must； can't
B：must； mustn't
C：can't； can't
D：can't； mustn't
答案(点此获取答案解析）
A
， 
， 
，0中，整式的个数是( )