[单选题]由发电车柴油发电机组集中供电的列车，供电电压为（　）交流电。
A.110V
B.220V
C.380V
D.380V/220V

{{B}}Keeping the Net Secure{{/B}}
On September 11 traditional telephone providers did a heroic job of struggling to restore service. When the World Trade Center towers fell, they severely damaged a Verizon central office with 350,000 voice lines and 3.5 million data circuits carrying the financial information that is the lifeblood of Wall Street firms. Verizon employees and those of many other telecommunications carders worked night and day, alongside the firemen, the police, and volunteers, at their own recovery job. In about a week they had rerouted some two million data circuits, restored switches, and installed temporary power supplies. The other 1.5 million circuits originated in buildings that no longer exist.
In the days after the attack the number of voice calls in the five boroughs of New York City doubled, from the normal 115 million a day to more than 230 million. For the