Some kids cant sit still for long. They have a hard time paying attention to just one thi

Some kids can't sit still for long. They have a hard time paying attention to just one thing. They're easily distracted(分神).They can get very impatient. They hate standing in line or waiting for their turn in a game or activity. They get bored pretty fast. They may also be impulsive—saying the first thing that es to mind or interrupting someone else who's talking.
For certain kids, this problem is so severe(严重) that doctors have a name for it: attention deficit hyperactivity disorder, or ADHD. Perhaps as many as 1 out of every 20 kids under the age of 18 have characteristics of ADHD. Often, these kids have trouble getting through school and face other difficulties later in life.
Rizzo started developing the Virtual Classroom in 1999.He wanted to see if he could use it as a tool for testing and treating kids who have attention disorders.
To diagnose(诊断) ADHD, doctors typically test patients by giving them tasks that require attention. As part of one classic test, you watch letters flashed on a puter screen. Every time you see the letter “A” followed by the letter “X”,you have to press the space bar. If you're paying close attention, you'll register all the times this bination occurs. If not, you'll miss some.
The Virtual Classroom makes these tests more efficient, Rizzo says. In one experiment, he gave a group of kids the classic “A-X” test. Instead of looking at a puter screen in a doctor's office, though, the kids wore headsets that made it look like they were taking the test in a classroom.
“Basically what we found,”Rizzo says,“is that, in 20 minutes of testing with virtual reality,we replicated(复制) a finding that usually requires a couple hours of standard testing with puter screens in the psychologist's office.”
【小题1】The first paragraph mainly tells us     .A．how to find a patient with ADHDB．the behavior of some kids with ADHDC．kids with ADHD cannot sit still for a long timeD．kids with ADHD are easily distracted【小题2】 Perhaps as many as      kids have characteristics of ADHD. 
A. one out of every twenty kids
B. five percent kids less than 18 years old
C. one out of twenty kids at the age of 18
D. five percent kids more than age of 18
【小题3】 In the experiment, patients need to press the space bar, when     .A．see letters A following XB．first see A then see BC．see letter X and AD．see letters A followed by X【小题4】The main idea of the last paragraph is     .A．in virtual classroom, we finish the test in 20 minutesB．the standard test with puter screen usually costs several hoursC．the experiment is easy to doD．the result of the experimentB