Thirteen vehicles lined up last March to race across the Mojave Desert，seeking a million in prize money. To win，they had to finish the 142mile's race in less than 10 hours.
Teams and watchers knew there might be no winners at all，because these vehicles were missing a key part—drivers.
DARPA，the Defense Advanced Research Projects Agency，organized the race as part of a push to develop robotic vehicles for future battlefields. But the Grand Challenge，as it was called，just proved how difficult it is to get a car to speed across an unfamiliar desert without human guidance. One had its brake lock up in the starting area. Another began by throwing itself onto a wall. Another got tied up by bushes near the road after 1.9 miles.
One turned upside down. One took off in entirely the wrong direction and had to be disabled by remote(远距离的) control. One went a little more than a mile and rushed into a fence；another managed to go for six miles but stuck on a rock. The “winner，” if there was any，reached 7.8 miles before it ran into a long，narrow hole，and the front wheels caught on fire.
“You get a lot of respect for natural abilities of the living things，” says Reinhold Behringer，who helped design two of the car size vehicles for a company called SciAutonics. “Even ants(蚂蚁) can do all these tasks effortlessly. It's very hard for us to put these abilities into our machines.”
The robotic vehicles，though with necessary modern equipment such as advanced computers and GPS guidance，had trouble figuring out fast enough the blocks ahead that a two-year-old human recognizes immediately. Sure，that very young child，who has just only learned to walk，may not think to wipe apple juice off her face，but she already knows that when there's a cookie in the kitchen she has to climb up the table，and that when she gets to the cookie it will taste good. She is more advanced，even months old，than any machine humans have designed.
48.Watchers doubted if any of the vehicles could finish the race because ______.
A．they did not have any human guidance
B．the road was not familiar to the drivers
C．the distance was too long for the vehicles
D．the prize money was unattractive to the drivers
49.DARPA organized the race in order to ______.
A．raise money for producing more robotic vehicles
B．push the development of vehicle industry
C．train more people to drive in the desert
D．improve the vehicles for future wars
50.From the passage we know “robotic vehicles” are a kind of machines that ______.
A．can do effortlessly whatever tasks living things can
B．can take part in a race across 142 miles with a time limit
C．can show off their ability to turn themselves upside down
D．can move from place to place without being driven by human beings

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