下列施工测量仪器中，（）的主要功能是测量两点间的高差。
A.经纬仪
B.水准仪
C.全站仪
D.光电测距仪
参考答案：B
---I came to your office yesterday morning, but nobody was in.
--- Sorry, we _______ a meeting .
A．have had
B．are having
C．were having
D．had
钢轨探伤中，为了提高双35°探头的探伤灵敏度应尽量提高增益。
