Which of the following is part of the safety loop key switch bypass?

The holding brake relay is essential in the context of a safety loop key switch bypass. This relay plays a crucial role in ensuring that safety measures are maintained when the equipment is operating. In a safety loop, the holding brake relay contributes to the overall system's ability to stop the machinery in a controlled manner. If the bypass occurs, the relay ensures that the safety mechanisms remain functional and can initiate a safe stop if needed, thereby preventing potential accidents that could arise from unintentional operation.

The other options, while they may have significant functions in various control systems, do not directly relate to the specific task of providing controlled safety shutdowns in the context indicated by the question. The brake handle, for instance, is used for manual control without direct involvement in the relay operations, while the speed governor regulates engine speed and does not pertain to the safety lockout feature of the key switch bypass. The fuel management system manages fuel usage and efficiency but does not involve the immediate safety operations signified by the relay in the context of bypassing the key switch.