根据短文的内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Jealous of the kids at school who are smarter than you and seem to learn more quickly? Don’t worry.  小题1: 
  小题2: However, according to a recent study, IQ can rise—not just by one or two points, but by as many as 21 points!
Scientists have found that IQ changes are linked to changes in part of the brain called gray matter, which was seen to grow and become denser（更加密集）in the brains of people whose IQs improved greatly.
  小题3: One is to train your short-term memory. Previous research has proven that short-term memory is the basis for intelligence, so trying to recognize or retell something that you have seen or heard can help raise your overall brain power.   小题4: 
A good night’s sleep will also help improve your concentration.  小题5: It helps you stay focused for longer the next day.
Scientists have also found that exercise helps. Walking 30 minutes a day five times a week and doing exercise will help you become more knowledgeable—as well as healthier and fitter.

A．There are several ways of increasing your brain’s gray matter.

B．Your brain deals more efficiently with things you truly like.

C．With a bit of brain training, the chances are that you can be as smart as they are.

D．So maybe it’s a good idea to get your brain in training right away.

E. Getting enough sleep is like pushing the reset button in your brain.
F. The more you work on it, the better you will become.
G. People used to assume that a person’s IQ was unchangeable.