trolley bus,unrest

为什么旧金山的电车叫cable car而不是trolley bus?
edmonton transit system trolley bus 1979 view - vintage postcard
budapest trolley bus
无轨电车old_trolley_bus_-_geograph.org.uk_-_351325
trolley bus 无轨电车streetcar 有轨电车 (英式为tram)school bus