17．Work your brain!
Between 2 and 3 pounds of wonder，it controls everything we say，do or think，who we are and what we care about，the way we walk or laugh or figure out things，what we like and the talents we possess，how we see and talk and run and jump and process our food．
The brain uses 20 percent of our body's oxygen and 20 percent of its blood．Somewhere within its protein，fat，100，000 miles of blood vessels and 100 billion nerve cells，it helps us remember where we put our gym shoes．Change our temperature so we don't die because of the heat or cold．Speed us up or slow us down．Help us choose between orange juice or orangeflavored drinks．
Its complexity is stunning，far beyond anything most of us can imagine．To keep this work of art as polished as possible we need to eat right，exercise and keep mentally stimulated．
Good nutrition help s brain cells communicate with each other．Exercise stimulates a hormone in our brain that improves memory．Mental stimulation keeps you sharp even as you age．
"It's very important that we tell people to be physically active and mentally active，"said neurologist Malcolm Stewart．
"People cannot stop aging，but you're able to reduce the damage； you're able to keep the function up．"
Following are Dr．Stewart's advice for improving brain health：
l Nutrition
Avoid fast food．Follow the old adage（格言）：For breakfast，eat like a king； for lunch，like a
queen； for supper，like a beggar．
l Exercise
Do a combination of stretching aerobic and musclestrengthening every day．
l Mental games
Try to have a sense of hope about the future．Do puzzles．Listen to music．Reach out to others to make their lives better．
54．The purpose of the author in writing this passage is toB．
A．inform us how the brain works
B．give us advice on how to keep the brain healthy
C．tell us that the brain plays an important role in our lives
D．show how special the brain is to us
55．The word"stunning"in Paragraph 5 meansD．
A．interesting
B．strange
C．significant
D．amazing
56．According to the text，more exerciseB．
A．keeps our mind sharp
B．helps improve our memory
C．gives our brain a rest
D．is good for brain cells communicating with each other
57．In order to keep brain healthy，we should avoidC．
A．eating a good lunch
B．doing puzzles
C．eating a large supper
D．taking aerobic exercise．
