Which item is essential to carry when transporting hazardous materials?

Answer: B — The appropriate emergency response guidebook

When transporting hazardous materials, it is essential to carry the appropriate emergency response guidebook. This guidebook provides critical information on how to respond effectively to emergencies involving hazardous substances. It outlines safety measures, first aid procedures, and details specific to various types of hazardous materials, which are vital for ensuring the safety of the driver, emergency responders, and the public in case of an incident. Having this guidebook readily available allows transport drivers to quickly access necessary procedures and protocols, potentially mitigating risks and managing hazardous situations more effectively. While other options such as road maps, the driver's license, and insurance paperwork are important in their own contexts, they do not offer the immediate safety guidance and emergency procedures required when dealing with hazardous materials.