[单项选择]Learning disabilities are very common. They affect perhaps 10 percent of all children. Four times as many boys as girls have learning disabilities.
Since about 1970, new research has helped brain scientists understand these problems better. Scientists now know there are many different kinds of learning disabilities and that they are caused by many different things. There is no longer any question that all learning disabilities result from differences in the way the brain is organized.
You cannot look at a child and tell if he or she has a learning disability. There is no outward sign of the disorder. So some researchers began looking at the brain itself to learn what might be wrong.
In one study, researchers examined the brain of a learning-disabled person who had died in an accident. They found two unusual things. One involved cells in the left side of the brain, which control language. These cells normally are white. In the learning-disabled person, however, these cell
A. many factors account for learning disorder
B. a learning-disabled person shows no outward signs
C. reading disabilities are a common problem that affects 10 percent of the population
D. the brain activity of learning-disabled children is different from that of normal children