为什么我国冬季气温南北差异大？
参考答案：
北方太阳高度比南方小；北方白昼比南方短；寒冷的冬季风对北方影响大。
56. It is impossible for so workers to do so work in a single day.
A．few; much
B．few; many
C．little; much
D．little; many
可参与直接凝集反应的抗原是（）.
