When a handheld video game runs out of power, all you have to do is plug it in and charge it up. Within a few years, some of you might do the same thing with mom's car. Automobile companies are developing vehiclesthat will plug into electricsockets , just like many laptops, digitalcameras, cell phones and small video game players do. Called "plug-inhybrids ," these cars will get most of their power from electricity. Their drivers will rarely haveto stop at gas stations. The technology is more than just cool. In our automobile-filled world, plug-in vehicles could reduce the amount of gasoline we use. That gas is made from crude oil, which has been kept rising in cost. Plus, driving around in these hybrids may even help the environment. Gas-burning cars produce a lot of carbon dioxide, a type of greenhouse gas. These gases stay in the atmosphere, where theytrapheat and cause global warming. The first company-produced plug-in hybrids could hitthe roads by 20l0. But engineers still have a lot of work to do to make the technology practical and inexpensive. Batteries are the biggest challenge. In the plug-in-hybrid world, Li-ion batteries are getting the most attention. These batteries can store a large amount of energy in a small package, and they last a ly long time between charges. Li-ion batteries are standard in laptops, cell phones, heart devicesand similarportabledevices. But because cars are so big and heavy, it would still require a suitcase-sized Li-ion battery to power about l2km of driving. What's more, the batteries are extremely expensive. "A car filled with batteries could go a long distance," says Ted Bohn, an electrical engineer in prefix = st1 /Chicago. "But it couldn'thaul any people, and it would cost $l00,000." So researchers need to figure out how to make batteries smaller and cheaper, among other questions. "The answers don't exist yet," Bohn says. "As a kid I thought someone someplace knows the answer to everything. All of these questions haven't been decided. That's what... The writer wrote this passage with the purpose of _ . A) how to charge the handheld video game up B) explaining a newly-developed battery C) introducing a new car D) telling us how to make the new battery cheaper
A:
C