单项选择题

Villages in developing countries often lack many things. Books, clean water, electricity. These shortages are 1 to 2 But a 3 kind of shortage is not easy to see. That is a shortage of 4 Many villages have no doctors, engineers or scientists. They have no one who knows 5 to treat unusual medical problems or design a new expert system. There"s a way to ease these problems. They can do it with 6 . In the past few years, computer scientists around the world 7 8 they call expert systems. An expert system is a special kind of computer program. In some 9 , it can take the place of a human expert. For example, an expert in 10 system can help 11 a sick person. A question appears on the computer screen, "Is the person hot" You tell the computer either yes or no. The computer asks 12 questions. "Has the person lost any blood" "Can the person move normally" You 13 The computer continues to ask questions 14 it has enough 15 to make a decision. Then it tells what 16 or other treatment is needed. In this way the expert system takes the place of a 17 Another kind of expert system takes the place of an engineer. It 18 the flow of water in a river. It tells if a dam can be built 19 the river. It also tells 20 electricity can be produced. Still other kinds of expert systems help solve problems for farmers and owners of small businesses.

A.stops
B.understands
C.measures
D.makes