Final answer:
Water-resistant lithium-based grease should be used to lubricate the rack and slide path of a sliding fifth wheel due to its ability to handle heavy loads and resist washout in wet conditions.
Step-by-step explanation:
The correct lubricant to use for the rack and slide path of a sliding fifth wheel is c) Water-resistant lithium-based grease. This type of grease is specifically formulated to withstand the heavy loads and environmental conditions typically associated with the operation of fifth wheels. Water-resistant lithium-based grease provides excellent adhesion and will not wash away under wet conditions, ensuring proper lubrication and protection against wear and corrosion over time.