—Look! It ________________ be Kitty in the classroom.
—It ________________ be her. Because I saw her in the library a short time ago.
A:may; mustn't
B:can; can't
C:must; can't
D:mustn't; can
直线l经过A2,1,B1,m2m∈R两点,那么直线l的倾斜角的取值范围( )
请画出如图所示中球所受的重力和支持力的示意图。