单项选择题

Google is talking to auto makers about how to bring its self-driving-car technology to market, executives said Tuesday. Project director Chris Urmson said a self-driving car is probably still six years away. But, he added, "We are thinking now about how to bring this car to market."
There is a lot of "debate internally about how automobiles can use this technology," said Sebastian Thrun, the original leader of Google"s autonomous car project. "There will be a time when a significant number of cars will carry Google technology."
Google"s co-founder Sergey Brin—Urmson"s boss—said roughly a year and a half ago that Google"s self-driving car was about five years away. Urmson said on Tuesday that he is working on a six-year timeline, based on when his 10-year-old son turns 16 and will be able to drive in California. Bryant Walker Smith, a fellow at Stanford University"s Center for Automotive Research, said it can take up to six years to design and build a new car. Smith said any self-driving car ready in six years would likely be "limited in terms of capability, availability , or geography."
Google"s car looks like a regular vehicle but it uses multiple sensors and map data in real time to understand where it is and maneuver through streets and highways without human intervention. The project started in 2009 and became an early part of Google X, the company"s research lab for risky, long-term initiatives. Some on Wall Street are concerned about Google"s increased focus on these projects; however, they also give the company a chance to expand into huge new markets, such as autos.
Urmson said Google"s autonomous cars are expensive, but he declined to be specific. That"s partly due to the laser sensor perched on top of the vehicles, which is made by Silicon Valley-based Company Velodyne. About 150 of these laser devices are produced a year, which increases the price of the component, Urmson explained.
Besides, Arturo Corral, one of Google"s test drivers, said weather is a serious challenge. In heavy rain, the system asks drivers to take back control of the car, Corral said. Google has not tested the vehicles in snow yet. "We still have a long way to go," he added. Google"s co-founder estimated that it may take ______ to bring Google"s car into reality.