Final answer:
A highway tanker with reinforcing rings is used to carry flammable liquids, as these rings strengthen the tank against internal pressure.
Step-by-step explanation:
A highway tanker with a smaller-diameter tank featuring several reinforcing rings around the circumference is typically designed to transport flammable liquids. These reinforcing rings add structural integrity to the tank, allowing it to safely contain the high pressure that can build up with flammable materials such as gasoline or other petroleum products. Such tankers are subject to stringent transportation regulations due to the hazardous nature of their cargo.