单选题Directions : There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice and mark the corresponding letter on Answer Sheet 2 with a single line through the centre.
Questions are based on the following passage.
For years there have been endless articles stating that scientists are on the verge of achieving artificial intelligence, that it is just around the comer. The truth is that it may be just around the comer, but they haven't yet found the right clock.
　　Artificial intelligence aims to build machines that can think. One immediate problem is to de- fine thought, which is harder than you might think. The specialists in the field of artificial intelligence complain, with some justification, that anything that their machines do is dismissed as not being thought. For example, computers can now play very, very good chess. They can't beat the greatest players in the world, but they can beat just about anybody else. If a human being played chess at this level, he or she would certainly be considered smart. Why not a machine The answer is that the machine doesn't do anything clever in playing chess. It uses its blinding speed to do a brute-force (残忍的) search of all possible moves for several moves ahead, evaluates the out- comes and picks the best.
　　Humans don't play chess that way. They see patterns, which computers don't.
　　This wooden approach to thought characterizes machine intelligence. Computers have no judgment, no flexibility, no common sense. So-called expert systems, one of the hottest areas in artificial intelligence, aim to mimic the reasoning processes of human experts in a limited field, such as medical diagnosis or weather forecasting．There may be limited commercial applications for this sort of thing, but there is no way to make a machine think about anything under the sun, which a teenager can do. The hallmark (特征) of artificial intelligence to date is that if a problem is severely restricted, a machine can achieve limited success. But when the problem is expanded to a realistic one, computers fall flat on their display screens. For example, machines can understand a few words spoken individually by a speaker that they have been trained to hear. They cannot understand continuous speech using an unlimited vocabulary spoken by just any speaker.From the passage we know that the author__________

A．thinks that scientists are about to achieve artificial intelligence
B．doubts whether scientists can ever achieve artificial intelligence
C．does not think that scientists have found real artificial intelligence
D．is sure that scientists have achieved artificial intelligenc