Final answer:
The correct method for transporting a large boulder is to ensure it is properly secured using the appropriate devices, positioned for optimal balance on the vehicle.
Thus the correct option is B.
Step-by-step explanation:
When transporting a large boulder on a flatbed vehicle, the correct choice is b) Make sure it is properly secured. This means using proper securing devices such as chains, straps, or winches that are designed to handle the weight and size of the boulder. Ropes might not be sufficient unless they are specifically rated for the weight and type of load.
Positioning a heavy load like a large boulder should be based on the vehicle's load balance principles, usually centered and close to the front of the flatbed for better weight distribution and to avoid affecting the vehicle's handling. Ensuring that the boulder is secured prevents it from shifting or falling off during transport, which could lead to dangerous situations both for the vehicle's driver and other road users.