脉冲仓顶除尘器是由（）组成。
A、上箱体；
B、下箱体；
C、清灰系统；
D、除尘系统。
参考答案：A, B, C
Oil prices have risen by 32 percent since the start of the year, ____ a record US$57,65 a barrel on April 4. [ ]
A. have reached
B. reaching
C. to reach
D. to be reaching
谈判媒介
