—Shall we________to attend the meeting________at the end of this month?

—Sorry, I don't know.[ ]

A. ask; holding

B. ask; to hold

C. be asked; held  

D. be asked; to be held

当空调系统工作正常时，膨胀阀与蒸发器间的冷媒状态应是低压液态的冷媒