Practice question What does the X endorsement combine? Tank Vehicle and Hazardous MaterialsPassenger and School BusAir Brakes and DoublesGeneral Knowledge and Combination Vehicles Answer: A — Tank Vehicle and Hazardous Materials The correct answer is shown above. Try the full quiz for additional practice. Practice more: Mississippi CDL HazMat Endorsement Test Practice Questions - Mississippi CDL Hazardous Materials Endorsement Test Exam →