Green squares with odd numbers on day marks should be kept on which side when proceeding upstream?

Green squares with odd numbers indicate specific navigational markers that are part of the lateral system of navigation. When a boat is proceeding upstream—meaning it is moving against the current or tide—these markers should be kept on the left, or port side, of the vessel. This is consistent with the standard rules of navigation that dictate how to interpret these markers.

Understanding the significance of these markers is essential for safe navigation. The odd-numbered green square markers help indicate the channel's limits and guide boaters safely through the waterway. By keeping these markers to the left while navigating upstream, boaters can ensure they are within the designated channel and avoid hazards that could be found on the right side of the waterway.

The other options refer to different sides or positions of the vessel where the markers are not meant to be kept when navigating upstream, leading to potential navigational confusion or hazards.