three times，but she still couldn’t follow what the old man said．

A．Having told

B．Having been told

C．She had been told

D．Though he had been told

在电解水的实验中，若与电源正极相连的试管内收集了nL气体，则与电源负极相连的试管内理论上可以收集到的气体的体积为 [ ]

A、nL             

B、2nL          

C、0.5nL            

D、0.8nL