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 142-mile race in less than 10 hours . Teams and watchers knew there might be no winner at all , because these vehicles were missinge 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  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 Sci-Autonics . "Even ants   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 . Watchers doubted if any of the vehicles could finish the race because_.
they did not have any human guidance the road was not familiar to the drivers the distance was too long for the vehicles the prize money was unattractive to the drivers
Question: 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 142-mile race in less than 10 hours . Teams and watchers knew there might be no winner at all , because these vehicles were missinge 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  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 Sci-Autonics . "Even ants   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 . 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
Answer: