Which vessel should display yellow lights when towing?

Towing Lights on Commercial Vessels When commercial vessels are towing or pushing a barge, they display one or more yellow lights in place of a sternlight. There may be an unlit space of several hundred yards between the lights displayed on the bow and stern of the composite formed by the commercial vessel and its barge(s). read more

The answer is D. Commercial towing boats like those that tow barges, etc. run a yellow light to show that they are towing and to warn other boats not to try to pass behind them and the "boat" following them. read more