A、The density of some gray matter increased. B、The density of some gray matter decreased. C、The area of the gray matter became b

A study in Norway has found that students who stayed in school longer than others their same age scored higher on intelligence tests.
     (16)In the middle of the 1950s, the government began requiring students to attend school until the age of 16 instead of 14. Communities had almost 20 years to make the change. So some students went to school for 7 years while others went for at least 9 years. This difference gave researchers the chance to see if the additional schooling had any effect on intellectual development. The researchers compared the test results of 107, 000 young men to their years of school. Taryn Ann Galloway is a researcher at the University of Oslo.(17)She says that students who attended school for 9 years scored 7 points higher than those who attended for 7 years. Those who went for 8 years scored about 4 points higher.
    Another recent study, in the journal Nature, found that IQ scores can rise or fall during the teenage years.(18)In 2004, researchers from University College London tested 33 young people ages 12 to 16. They repeated the tests 4 years later. They found increases or decreases of as much as 20 points. Both times, they also took structural brain scans using MRI, magnetic resonance imaging.(19)The study found that as IQ scores increased, so did the density of gray matter in some areas of the students’ brains. Professor Cathy Price says the differences in performance could be the result of some teens being early or late developers. But she says it is equally possible that education played a part.
16. What new policies did Norway government launch in the middle of 1950s?
17. What did Galloway find in her research?
18. Who are the subjects of the study in the journal Nature?
19. What is the change in people’s brains when their IQ scores increased?