Lesson14 Dolphins
Many people have experienced the joy of standing on a moving ship and watching a group of dolphins swim alongside． Dolphins are not only playful animals but they are also highly intelligent． They are mammals that can be found in most of the world's oceans as well as in fresh water．
Dolphins can swim at speeds of up to 56 KPH and they can dive to depths of 200 meters and stay underwater for 5-8 minutes without resurfacing for air． They are well-known for the unique clicking sound they use like sonar to locate food as well as obstacles． Every dolphin has its distinctive individual whistling sound used for communication．
When dolphins sleep， they sleep in a semi-alert state by resting one side of their brain at a time． They will help sick or injured dolphins as much as they can， and they act as a team if there is danger．
It is because of these and other human-like qualities that people have a special feeling for dolphins．

dolphin ? 海豚
mammal ? 哺乳动物
resurface ? 重新露面
unique ? 独特的
sonar ? 声波定位仪
obstacle ? 障碍物
distinctive ? 与众不同的
whistle ? 吹口哨
semi-alert ? 半警惕的

海豚
许多人一定会有这样开心的经历——站在航行的船上，看着一群海豚从旁边游过。海豚不仅是一种有趣的动物而且极其聪明。海豚是哺乳动物，人们可以在世界上大多数的海洋和淡水中找到它。
海豚的游速可以达到每小时五十六公里，可以潜到两百米深的地方，在水下待五到八分钟而不浮出水面。海豚另一有名的特点是它们可以使用独特的像声波定位器一样的敲击声来确定食物和障碍物的位置。每一头海豚都有自己与众不同的声音，他们靠发出这种声音互相交流。
当海豚睡觉时，它们处于半惊醒状态，每次只休息大脑的一半。它们会尽力帮助生病或受伤的海豚；在遇到危险时，它们会相互协助。
正是因为这些及其他类似于人的特性，人们对海豚有着特殊的感情。