—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
函数y=1+cosx的图象( )
10-5= ____
4+10=____
13-13=____
18-6=____
在图上确定方向的基本方法是:上____、下____、左____、右____。