When steering on a range, if the top and bottom marks are in line, it means you are ____________________________________ of the center of the channel.

When the top and bottom marks are in line while steering on a range, it indicates that you are positioned directly on the centerline of the channel. This alignment signifies that you are on a safe navigational course with reference points providing guidance for maintaining the appropriate heading. Properly aligning with the range marks is crucial for safe navigation, as it ensures that vessels remain in the designated navigable water area, thereby reducing the risk of grounding or collision. The other options suggest being off to the sides or away from the center, which would not result in the top and bottom marks appearing aligned; therefore, they do not reflect the scenario of being on the centerline.