Which of the signals listed is required to be displayed during the day while bunkering?

The requirement to display a red flag during the day while bunkering is rooted in maritime safety practices. This visual signal is primarily intended to alert nearby vessels that bunkering operations are taking place, which can present hazards. The red flag serves as a clear and easily recognizable indication that caution should be exercised in the vicinity of the operation to avoid accidents or potential incidents.

Bunkering involves transferring fuel, which inherently carries risks such as spills, leaks, and fire hazards. Therefore, the use of the red flag adds an essential layer of safety by communicating to other vessels and personnel that they should keep a safe distance during this potentially dangerous operation.

In contrast, the other signals mentioned in the options either do not convey the proper warning or do not fulfill the regulatory requirements concerning operations like bunkering. For example, the yellow flag may indicate a cautionary signal but does not specifically denote the same urgency as the red flag in this context. The combination of red and yellow flags or the use of a red light may not be appropriate for the day signal requirement as stipulated by maritime regulations.