其他条件不变，精馏塔底温度降低，对精馏操作的影响有（）。
A、塔顶温度降低
B、塔压升高
C、塔顶产品纯度提高
D、塔底产品纯度提高
参考答案：A, C
While we were listening to the speech attentively, a voice ________ to announce the result of the election
A．broke in
B．broke down
C．broke up
D．broke off
总结是与报告相对应的机关常用文书。 ( )
