At least how many tests were carried out by the scientists referred to in this passage

How many teeth did the dentist take out?

A:dig
B:draw
C:pull
D:extract

共用题干
Learning Disabilities
Learning disabilities are very common.They affect perhaps 1 0 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 cells were gray.The researchers also found that many of the nerve cells were not in a line the way they should have been.The nerve cells were mixed together.
The study was carried out under the guidance of Norman Geschwind,an early expert on learning disabilities, Doctor Geschwind proposed that learning disabilities resulted mainly from problems in the left side of the brain. He believed this side of the brain failed to develop normally.Probably,he said,nerve cells there did not connect as they should.So the brain was like an electrical device in which the wires were crossed.
Other researchers did not examine brain tissue.Instead,they measured the brain's electrical activity and made a map of the electrical signals.
Frank Dully experimented with this technique at Children's Hospital Medical Center in Boston.Doctor Dully found large differences in the brain activity of normal children and those with reading problems.The differences appeared throughout the brain.Doctor Dully said his research is evidence that disabilities involve damage to a wide area of the brain,not just the left side.

According to the passage we can conclude that further researches should be made______.
A:to help learning-disabled children to develop their intelligence
B:to study how children learn to read and write,and use numbers
C:to investigate possible influences on brain development and organization
D:to explore how the left side of the brain functions in language learning

What is referred to as the“general appearance”in this passage is________.

A.how many broad windows a room has,through which sunlight might come in
B.the size of a room
C.whether there are beautiful walls in a room
D.what the room looks like