1.   And at low speeds, when gas engines are inefficient, the battery does the work.

2.   As it happens, electric motors provide torque more efficiently than a gas engine.

3.   At a stoplight, where a gas engine is at its least efficient, the Prius engine turns itself off, saving more gas.

4.   - In highway cruising, the gas engine takes over, supplemented by electric power.

5.   - Under full acceleration, both the electric motor and the gas engine share the load.

6.   - When pulling away from a stop or under light acceleration, only the electric motor is doing the work, with the gas engine shut off.

7.   A sophisticated computer system constantly regulates the gas engine, electric motor and generator, using each in the most efficient way possible.

8.   But that does not mean that the gas engine must work double time.

9.   But when the car speeds up, the gas engine takes over.

10.   Gas engine?