Which of the following are recommended lubricants for heavy-duty truck U-joints?

A) lithium-based grease with EP additives
B) NLGI grade 1 or 2 grease
C) NLGI grade 3 or 4 grease
D) both A and B

Lithium-based grease with EP (Extreme Pressure) additives is recommended for heavy-duty truck U-joints because it provides excellent protection under high pressure and shock loading conditions. NLGI (National Lubricating Grease Institute) grade 1 or 2 grease is also suitable for these applications due to its appropriate viscosity and performance characteristics under a wide range of temperatures, making both A and B correct choices.