Are you preparing for a big test? If so, you may want to go play some basketball in between hitting the books. Doctors are starting to find more and more information that suggests a connection between exercise and brain development. Judy Cameron, a scientist at Oregon Health and Science University, studies brain development. According to her research, it seems that exercise can make blood vessels（管）, including those in the brain, stronger and more fully developed. Dr. Cameron claims this allows people who exercise to concentrate better. As she says, "While we already know that exercise is good for the heart, exercise can really cause physical changes in the brain."

The effects of exercise on brain development can even be seen in babies. Babies who do activities that require a lot of movement and physical activity show greater brain development than babies who are less physically active. With babies, even a little movement can show big results. Margaret Barnes, a pediatrician（儿科医生）, believes in the importance of exercise. She thinks that many learning disabilities that children have in elementary school or high school can be traced back to（可追溯到） a lack of movement as babies. "Babies need movement that stimulates their five senses（感官）. They need to establish a connection between motion（动作）and memory. In this way, as they get older, children will begin to associate（联系） physical activity with higher learning," says Margaret.

Older people can beef up（加强） their brains as well. Columbia University studied a group of seniors ranging in age from（从...排列到） seventy to seventy-nine. Their study showed a short-term memory increase of up to 40 percent after exercising just three hours a week. The exercise does not have to be very difficult, but it does have to increase the heart rate. Also, just like the motion for infants（婴儿）, exercise for older people should involve some complexity. Learning some new skills or motions, such as with yoga or tai-chi, helps to open up memory paths in the brain that may not have been used for a long time.

For most people, any type of physical activity that increases the heart rate is helpful. The main goal is to increase the brain's flow of blood. And your brain can benefit from as little as two to three hours of exercise a week.

1．What is the main idea of this reading?

A．How to exercise                                  B．How exercise helps the brain

C．How to get good scores on a test          D．How the brain can change

2．According to the reading, what is the connection between exercise and brain development?

  A．Exercise makes us stupid．                  B．The brain needs special mental exercise.

  C．The more exercise, the bigger the brain  D．Physical exercise helps us think better.

3．The minimum（最小）amount of exercise required to gain any benefit is.

A．three hours per week                          B．40 hours per week 

C．three hours per day                             D．40 hours per month

4．Why is yoga recommended for seniors?

A．It is easy on joints.                               B．It can be done in groups.

C．It does not increase the heart rate.         D．It includes learning new motions.