题干
— I saw Mr. Green at school this morning.
— No, it _____ him. He flew to Canada last week.
A：can be
B：must be
C：can't be
答案(点此获取答案解析）
C
— I saw Mr. Green at school this morning.
— No, it _____ him. He flew to Canada last week.
A：can be
B：must be
C：can't be
与
互相垂直,则
=( )
