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 still used to deliver energy from the bakeries 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. Why do electric cars still waste much of the energy

A. Because they have replaced the internal-combustion engine with bakeries.
Because they still use mechanical paas to transfer energy to the wheels.
C. Because they use magnets in the wheels which add weight to the car.
D. Because batteries are not powerful enough to drive the cars.