The correct answer is B) once a month. The reasoning for this is based on the regulations outlined in Title 46 of the Code of Federal Regulations (CFR), which governs the U.S. Coast Guard licensing and documentation requirements. Specifically, 46 CFR 199.180(b) states that "If reasonable and practicable, rescue boats must be launched with their assigned crew at least once every month and whenever the crew is assembled for abandon ship drills or training." The other options are incorrect because launching rescue boats less frequently, such as once a year (A) or twice a year (C), would not meet the regulatory requirement of monthly testing. Launching them once a week (D) would exceed the minimum requirement.