Final answer:
The student's question seems to be about transportation regulations related to 7D vehicles, but the provided reference information is about an airline and human height statistics, hence no definitive answer can be given.
Step-by-step explanation:
The student's question regarding the maximum size vehicle that can be used as a 7D vehicle appears to be related to specific regulations or guidelines, likely in the context of transportation or driver qualifications. Unfortunately, based on the provided reference information, which discusses the 757 airliner's capacity and the average height of doors and men, it seems there might be some confusion as the reference information does not correlate to the question about 7D vehicles. A 7D vehicle typically refers to a type of small passenger vehicle used for transporting students, and the maximum passenger and seat capacity can vary based on state or country regulations. However, without specific regulatory context or clear guidelines, it is not possible to give an accurate answer to the maximum number of passengers and seats for a 7D vehicle.