Generally speaking，prices of daily goods ________ through the Internet are lower than store prices.

A．to buy

B．are bought

C．buying

D．bought

对于由排放源排放的粒径大于15μm的颗粒物，地面浓度采用( )模式计算。

A．气体模式

B．斜烟羽模式

C．虚点源模式

D．窄烟云模式