Question Poisonous fumes can enter a cab due to: Answers A defective exhaust system. Using the wrong type of fuel. A lack of oil in the engine. Explanation A faulty exhaust system is a serious safety hazard. It may allow poisonous fumes to enter the vehicle's cab or sleeper berth. Take a FREE Practice Test Now This questions appears in the following tests: Hawaii Knowledge Test Class A , Louisiana Knowledge Test Class A , Michigan Knowledge Test Class A , Mississippi Knowledge Test Class A , Alaska Knowledge Test Class B , South Carolina Knowledge Test Class B , Delaware Tank ,