A rider tries to board your bus carrying a car battery, with no hazmat label or declaration. What should you do?

AAMVA CDL Manual Section 4.2.2 "Forbidden Hazardous Materials," p. 4-2

Most hazmat risk on a bus doesn't come with a label, it comes from ordinary items riders don't think of as dangerous, like car batteries or a gas can. Drivers are the last line of defense, so the exam tests whether applicants know to intervene even without a hazard placard in sight.