管道由于污水、污物积聚造成输送效率降低，可以通过（）提高
A.提高起点站压力
B.增大输气量
C.通球清管
D.降低终点站压力
参考答案：C
The worker _______ in the factory has been fired. [ ]
A. having caught smoking
B. caught smoking
C. is caught smoking
D. caught smoked.
粒径小于1nm（）
A．胶体溶液
B．微乳
C．真溶液
D．混悬液
E．乳浊液
