Question 390Navigation General

The correct answer is A) the downstream end of an intermediate wall. The presence of two green lights in a vertical line indicates the downstream end of an intermediate wall within the lock. This configuration helps mariners identify the navigable passage through the lock structure. The other answer choices are incorrect because they do not accurately describe the meaning of this specific light configuration. B is incorrect as it refers to the navigable pass of a fixed weir dam, which is a different type of waterway structure. C is incorrect as two green lights do not indicate a double lockage in progress. D is incorrect as the lights do not mark the downstream end of the land wall, which is a different part of the lock system.