A high pressure tanker usually carries what type of material?

High pressure tankers are specifically designed to transport gases that are liquefied under high pressure, such as liquefied flammable gases. These gases include materials like propane, butane, and various industrial gases that must be kept under pressure to remain in a liquid state for transport. This is critical for safety and efficiency, as these gases have a tendency to expand and potentially create hazardous situations if not contained properly.

While other materials, such as compressed air and non-hazardous chemicals, might be transported in different types of tankers or containers, they do not require the high pressure tank specialized for liquefied gases. Solid waste, on the other hand, would not be transported in a high pressure tanker at all, as it does not necessitate the specialized containment that high-pressure systems provide. Thus, option B accurately identifies the type of material typically carried by high pressure tankers.