Dust storms most often occur in areas where the ground has little vegetation to protect ________of the wind.

A．from the effects

B．it the effects

C．it from the effects

D．the effects from it

物流系统战略的金字塔结构中，四个主要层次分别为：客户服务、物流战略结构层、物流战略执行层和（）

A.物流战略预测

B.物流成本

C.库存可得率

D.物流战略实施层