题目内容

“ Is David still here?” “No, I am afraid he isn’t. He___________ about 10 minutes ago.”

A. has left
B. has been leaving
C. left
D. was left

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I went to Sue's house, but she wasn't there.

A. She went out
B. She has gone out
C. She had gone out
D. She had been going out.

We were extremely tired at the end of the journey. ________ for more than 24 hours.

A. We have travelled
B. We have been travelling
C. We had travelled
D. We had been travelling

当平衡阀的阻力系数增大时，阀门的流量G（）

A. 增大
B. 减小
C. 不变
D. 以上都不对

平衡阀与普通阀门最主要的区别之一是（）

A. 检修时关闭平衡阀，关闭后不能复位
B. 传统阀门可显示流量值
C. 具有开度锁定装置
D. 平衡阀不能计算出开度值