For years there have been endless articles stating that scientists are on the verge of ach

ieving artificial intelligence that is just around the corner. The truth is that it may be just around the corner, but they haven't yet found the right block.

Artificial intelligence aims to build machines that can think. One immediate problem is to define 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 player 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 march of all possible moves for several moves ahead, evaluates the outcomes 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 imitate the reasoning processes of human experts in a limited field, such as medical diagnosis(诊断) or weather forecasting. There may be limited commercial application for this sort of thing, but there is no way to make a machine that can think about anything under the sun, which a teenager can do.

The characteristic 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 writer ______.

A．thinks that scientists are on the point of achieving artificial intelligence

B．is in the full conviction that scientists have the competence to achieve artificial intelligence

C．remains doubtful of the fact that scientists have found real artificial intelligence

D．predicts with optimism that achieving artificial intelligence is now near at hand