气轮机冲转时，真空会（）
A、上升
B、不变
C、下降
D、无法确定
参考答案：C
They have never been to Beijing, _____? [ ]
A. have they
B. haven't they
C. do they
D. don't they
将发酵液加水后，降低了发酵液中固形物的浓度及其发酵液的黏度，从而使发酵液的过滤速度（）。
A.提高
B.降低
C.相等
D.以上都不正确
