For towing vessels over 100 gross tons that are permitted to maintain a two-watch system, what percentage of the deck crew must be able seamen?

Correct Answer: Option A — 50%

For towing vessels over 100 gross tons operating on a two-watch system, 46 CFR 15.840 requires that at least 50% of the deck crew be Able Seamen. This ensures a sufficient number of qualified personnel are available to handle the vessel safely during all watch rotations and emergency situations.