单选题 Cars have traditionally been wasteful beasts. Every time a drop of gas explodes inside a cylinder(气缸), the energy gets passed along from the piston(活塞)to the crankshaft(曲轴), flywheel (飞轮), gearbox, drivetrain, and axles(轮轴). By the time the wheels actually turn, four fifths of the original energy has disappeared. The electric Car goes a long way toward reducing wasted energy by replacing the internal - combustion engine with batteries. Even so, electric cars destroy about 60 percent of the energy because mechanical parts are stiu used to deliver energy from the batteries to the wheels. Lately, though, engineers have come up with a far more efficient way to accomplish the same task: by using magnets in the wheels.
In traditional cars, four fifths of the original energy has been wasted by the time

• A. the gas explodes inside the cylinder.
• B. the energy gets passed along from the piston to the crankshaft.
• C. the energy was delivered from the batteries to the wheels.
• D. the energy is finally passed to the wheels.