--- Do we have to finish our homework this afternoon?
--- Yes, you .
A:must
B:can
C:may
D:need
与同纬度的长江中下游平原相比,青藏高原气温日较差大的原因为( )
①青藏高原距离太阳近 ②青藏高原比长江中下游平原太阳高度角大
③地势高,空气稀薄 ④白天太阳辐射强 ⑤云层厚 ⑥夜晚大气逆辐射弱