在瑞利散射条件满足的情况下，降水粒子集合的反射率因子只与降水粒子本身的（）和（）有关。
参考答案：尺寸；数密度
对于正常菌群的描述，恰当的是（）
A.正常菌群、宿主与外界环境间应维持动态平衡
B.一般情况下正常菌群对人体有益无害
C.口腔中的正常菌群主要为厌氧菌
D.可以降解食物残渣
E.即使是健康胎儿也携带正常菌群
Obviously, the word "arrangement" underlined in the third paragraph refers to the fact that ______.
A．he was arranged to speak about his involvement
B．a campaign was under way to promote the administration
C．he was paid for speaking on NCLB developments
D．some critics made an arrangement to criticize him
