Ground service bus has no power with external power available.
答案解析
解析：
现在让我们来看选项：
A. 地面服务总线没有电力，但是外部电源可以提供电力。
B. 地面服务总线在外部电源的情况下没有通电。
C. 外部电源供电时，地面服务总线断电。
根据题干，我们知道地面服务总线没有电力，但是外部电源是可用的。那么正确的答案应该是表达地面服务总线在外部电源的情况下没有通电，也就是选项B。
相关知识点：
外部电源可用时地面服务总线无电
相关题目
All text shall be prepared in one or two columns with justification at the discretion of the manufacturer; however, two columns are preferred for ease of reading.
Overhaul of any or all components in this chapter must be accomplished in a qualified shop in accordance with data supplied by the component manufacturer.
The manufacturer will have the option to include Time Limits/Inspections and Maintenance Checks in a separate manual, providing they are also placed in the Maintenance Manual.
在模拟高度时，确保ATC应答机处于备用状态， 否则可能会意外地产生虚假的TCAS目标。
查阅飞机记录本的故障记录以及中央DU或CDU上的相关故障信息，听取机组反映的故障, 报告故障并处理。
如果杆端轴承的径向磨损大于0.010英寸，在接下来的10个飞行循环或25个飞行小时内（先到为准）将其报废。
These ALIs are mandatory and cannot be changed or deleted without the approval of the FAA office that is responsible for the airplane model Type Certificate, or applicable regulatory agency.
Revisions, additions and deletions shall be identified by a vertical black line along the outside of the page opposite only that portion of the printed matter that was changed.
This method is recommended as minimizing errors of distribution, and also informs owners of the availability of systems and equipment.
The airplane general arrangement shall be illustrated with a scale line drawing consisting of plan, side and front views presented in a vertical sequence upon a single page.
