What do the designations A, B, C, D, and E grades of cargo define?

Correct Answer: Option D — flash point range and Reid vapor pressure index of petroleum products

Under 46 CFR Subchapter D, cargo grades are classified based on their flash point and Reid vapor pressure. These parameters dictate the specific handling, stowage, and safety requirements necessary to mitigate fire and explosion risks associated with the volatility and flammability of various petroleum products transported by tank vessels.