Machinery with ball bearings designed to be filled with grease should have the relief plug temporarily removed while grease is being added. This plug should remain out until the machinery has been operated and sufficiently warmed up to ensure that __________.

Correct Answer: Option D — a path of expansion is provided for the grease

Removing the relief plug during operation allows excess grease to be purged as the bearing reaches its normal operating temperature. This prevents internal pressure buildup and provides a necessary path for thermal expansion, ensuring the grease does not force its way past seals or cause overheating.