—Have you found the missing?couple in the mountain ?

—No, but we     hard to get in touch with them．     

A．have tried

B．have been trying

C．had tried

D．had been trying ．

变配电所的一切操作须得到（）的命令或许可。

A、电气负责人或供电部门调度员

B、电气负责人或供电部门领导

C、工程负责人或供电部门调度员

D、所长或值班长