AIDS is said________the biggest health challenge to both men and women in that area over the

past few years.  [ ]

A. that it is                  

B. to be

C. that it has been            

D. to have been

生产所需的基本原材料的( )是决定项目规模和经济效益的关键因素之一。

A．价格、环境及供应的稳定性

B．来源、价格及运输途径

C．来源、价格及环境

D．来源、成本及供应的稳定性