The draw span of a floating drawbridge may be marked with __________.

Correct Answer: Option A — a yellow light showing Morse Code (B)

Per the U.S. Aids to Navigation System, floating drawbridges are marked with a yellow light flashing Morse Code 'B' (dash-dot-dot-dot). This specific signal alerts mariners to the presence of the bridge span and distinguishes it from other navigational aids or fixed structures in the waterway.