紧急停机时，导水叶关闭的越快越好。
参考答案：错
After he finished school, he worked _____ a worker.[ ]
A. as
B. on
C. at
D. from
全淹灭火系统中，低压系统获得均相流的延迟时间不应大于（）。
A、20s
B、30s
C、60s
D、90s
