Lisa, now stop for a short break. You should know that you _____ all the morning. [ ]

A. are working

B. had been working

C. have been working

D. have worked

水银气压表的误差来源和缺陷主要有（）.

A.气压表温度的不确定度

B.真空不良

C.水银面的毛细下降

D.悬挂不垂直

E.气压表读数修正后的准确度