Final answer:
If driver B is injured in a collision between two vessels, driver A should respond by stopping their vessel and providing immediate assistance or calling for emergency help.
Step-by-step explanation:
In the event of a collision between two vessels, if driver B is injured, it would depend on the severity of the injury and the ability of driver A to respond. Driver A may stop their vessel and provide immediate assistance to driver B, calling for emergency help if necessary. They could also try to safely move both vessels to the side of the road and assess the situation. Ultimately, the specific actions taken would depend on the circumstances and the level of training and preparedness of driver A.