A short chain is usual attached to the back of a petrol tanker trailing behind it to ensure that the

• A.petrol tanker is balanced on the wh eel
• B.heat generated by friction in the engine can be conducted to the floor
• C.charges generated by friction in the tanker can be conducted to the earth
• D.the tanker moves slowly as the chain touches the floor
• E.chain produces sound for the resonance of the tanker engine