The correct answer is D) Flashing green. A flashing green light signal indicates that you have permission to enter the lock on the Ohio River. This is the standard signal used by the US Coast Guard to communicate to vessel operators that they are cleared to proceed into the lock. The other options are incorrect because: A) Steady red would indicate that you do not have permission to enter the lock and must stop. B) Flashing amber would indicate a caution or warning signal, not permission to proceed. C) Steady green is typically used to indicate that the lock is ready for vessels to enter, but a flashing green specifically communicates that you have been granted permission.