The main purpose of the passage is（）.

A．to tell us how expert drivers try to save gas
B．to tell us how to drive a car properly
C．to tell us how to make a car run smoothly
D．to tell us how to make your car consume less gas

Once it was considered good to keep the car engine idle a minute or two following cold stars. Today, with modern technology, the opposite is true. An engine operating under road conditions will warm up faster and run more efficiently than one that is idling. Idling just burns gas (on average, about a gallon an hour).

When you have a full tank of gas, park the car facing downhill is possible: this will pr any gas from coming out of the tank. Parking in areas of less or no sunlight helps pr the gas from steaming that would occur if you parked in the hot sun. Your car will stay cooler, too, and that means less gas consuming work for the air conditioner once the engine is started.

Stay away from wide-track tires if you want top mileage (耗油1升行驶的英里里程). Narrow-track tires produce less friction and thus rolling resistance. The same effect is achieved by adding three to five pounds above recommended pressure to each tire; while this won’t noticeably affect your car’s sliding quality, it will increase tire life and gas mileage.

Check tire pressure often, especially when the weather turns cold. The difference between winter and summer tire pressure can be as much as eight pounds. This could cost you two miles per gallon.