A:{1}
B:{2}
C:{0,1}
D:{1,2}
-- May I speak to Mr Smith?
-- , please. Here he comes.
人成熟的红细胞和精子的寿命都很短,这一事实体现了( )
如图,AB是⊙O的直径,点D在AB的延长线上,DC切⊙O于C,若∠A=25°,则∠D等于( )