垫圈流量计的孔板下游直接通大气，因此上流压力实际就代表（）。
参考答案：压力差
TW42UZ-B1车站电台的天线阻抗是（）。
A、50欧姆
B、75欧姆
C、100欧姆
D、125欧姆
I was ____ he received an invitation from his friend to visit Chongqing ____ he felt
on top of the world. [ ]
A. when; who
B. that ; that
C. when; that
D. that; where
