调节天平时，首先将天平放在水平桌面上，再把游码移到标尺的零刻线处，若指针静止时指在分度盘的右侧，这时应将平衡螺母向________调节
左
Mr Wang______an article on how to improve spoken English last month, but I don’t know whether he has finished it.
A．has written
B．wrote
C．had written
D．was writing
阀门外壳上标注的PN16DN25表明阀门的（）。
A.公称压力、公称直径
B.工作压力，外径
C.工作压力、进出口管径
D.公称直径、进出口管径
