运行油过滤器如何切换()。
A.慢开备用过滤器出口伐,待压力正常,直至全开。
B.视压差关运行过滤器出口伐。
C.运行过滤器排油后,交检修更换滤网。
参考答案:A, B, C
John didn't go to school __________ he was ill (病).[ ]
A. because
B. so
C. but
D. why
—It’s a long time________I saw you last.
—Yes, and what a pity it is now that it will be a long time________we see each other again.[ ]
A. before; since
B. since; when
C. since; before
D. when; before