-- Would you like to play football after school?
-- ________. I have a lot of homework to do.
A:I'm afraid not
B:Enjoy yourself
C:Take your time
D:It takes no time
正方体ABCD﹣A1B1C1D1,E、F分别是正方形A1B1C1D1和ADD1A1的中心,则EF和CD所成的角是( )
根据给出的程序语言,画出程序框图,并计算程序运行后的结果.