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在SAT阅读中我们常常会碰到一些常见的文化词条，有时候对这些知识不熟悉，会影响我们对整篇文章的理解，所以了解一些专有名词会提高我们的SAT阅读能力。今天我们主要给大家介绍两个词条，分别是Sonar和Dolphins。 1，Sonar Sonar is a technique that uses sound propagation to navigate, communicate or to detect other vessels. Sonar may be used as a means of acoustic location. The term sonar is also used for the equipment used to generate and receive the sound. The frequencies used in sonar systems vary from infrasonic to ultrasonic. 声纳一种利用水下声音传播来导航，联络或侦查其他船只的技术。它可用于声音定位。这个术语还指产生和接收声波的设备。声纳所使用的频率从次声到超声不等。 2，Dolphins Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 meters and 40 kilograms, up to 9.5 m and 10 ton. They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. Dolphins are considered to be amongst the most intelligent of animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture. | 
