What is a “rigid veicle”?

1. A vehicle body which exceeds the size of a normal vehicle.
2. A vehicle body in which the driver’s compartment is separated from the trunk.
3. A vehicle body with a partition between the driver’s seat and the passengers.
4. Correct answer: A vehicle body in which the driver’s compartment and the trunk comprise one unit.

WhyA combined vehicle has the driver's cab and the cargo area as one unit, like a van. If the cab is separate, it is an ordinary truck.