The rear of buses and trucks are provided with double wheels (tyres) or even more. This is provided in order to:
Increase pressure on ground
Decrease pressure on ground
Increase friction for efficient braking
The correct option is B Increase friction for efficient braking
The additional tyres or wheels at the back is used for better handling and efficient braking. The larger area of tyres provides more friction from the ground and therefore makes braking smoother.