Final answer:
In pre-stress concrete pipe joint assembly, a vegetable-based soap should be used to lubricate the gasket, as it is gentle on rubber materials and aids in effective joint assembly.
Step-by-step explanation:
In pre-stress concrete pipe joint assembly, the gasket should be lubricated with the correct type of lubricant to ensure a good seal and protect the integrity of both the gasket and the pipe surfaces. For this application, a vegetable-based soap is recommended as a lubricant. Petroleum-based products can deteriorate rubber and other gasket materials and should be avoided. Similarly, graphite and silicone lubricants are not suited for this task due to compatibility issues with the materials involved in pre-stressed concrete pipes. Therefore, the correct answer is D) Vegetable-based soap, which is known for being gentle on rubber materials and effective in facilitating the joint assembly.