观察鱼的外形，说出鱼与水中生活相适应的特征：
（1）鱼的体型呈______形，可以减少游泳时水的阻力．
（2）鱼的体色特点是：背部颜色较______，腹部颜色较______．在水中可以起到保护作用．
（3）填出图中各鳍的名称：
①______ ②______④______ ⑤______．
（1）身体呈梭形，在游泳时减少水的阻力．
（2）鱼身体的背面是深灰黑色，腹面是白色，不管是从上面还是下面看，不容易被敌害发现，是一种保护色，利于鱼的生活．
（3）鱼的身体长有①胸鳍、背鳍、②腹鳍、④臀鳍和⑤尾鳍是鱼在水中的运动器官．背鳍有保持鱼体侧立，对鱼体平衡起着关键作用；腹鳍起平衡作用； 尾鳍可以决定运动方向，又能同尾部一起产生前进的推动力； 臀鳍有协调其它各鳍，起平衡作用；胸鳍起平衡的作用，鱼的游泳是靠身体的尾部的摆动和各种鳍的协调作用而实现．
故答案为：（1）梭；（2）深；浅；（3）胸鳍；腹鳍；臀鳍；尾鳍
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 intricacies(复杂性)are stunning，far beyond anything most of us can imagine. To keep this work of art as polished(有光泽的) as possible we need to eat right，exercise and keep mentally stimulated(刺激)． Good nutrition helps brain cells communicate with each other. Exercise stimulates a hormone(荷尔蒙)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：
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