SAT阅读词条讲解

1、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.

海豚一种与鲸和钝吻海豚很接近的海洋哺乳动物，包括17属近40种。海豚体型差异大，从身长1.2米体重40千克到身长9.5米体重10吨不等。海豚遍布世界各地，主要在浅海大陆架活动。属食肉动物，主要食物是鱼类和鱿鱼。海豚被认为是自然界智商最高的动物之一。因其友善的'外表和貌似活泼的天性，被看作人类的好友。

2、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.