单体液压支柱备用量按使用量的（）备足。
A、30％
B、25％
C、20％
参考答案：A
自动喷水灭火系统
— What did Jack ask you just now?
— He wanted to know how long _____ when I reached the cinema. [ ]
A. had the film been on
B. the film had started
C. the film had lasted
D. had the film ended
