版本5

a、海豚是怎么定位的？有一个考点是它发出的波长频率会不会变化？答案在原文中可找到。 b、海豚利用click和emission来航海，并且能够区分船只的噪音，海底其它动物的声音，同伴的声音。比如一种虾，发出的声音很像是海豚发出的，人类一般不能区别出。[此处有题，答案是海豚对各种声音的辨别力比人类强。] 第二段开始讲述海豚具体的辨别声音的过程，比较复杂，大概是收到声音后再自己发出声音，然后通过回音等等来分辨。此处讲到海豚的emission是有规律的频率变化。[有题，问 emission的性质。答案是频率改变，但是有规律可循，可以预测。]

版本6

Echolocation - the location of objects by their echoes - is a highly specialized faculty that enables dolphins to explore their environment and search out their prey in a watery world where sight is often of little use. As sound travels four and a half times faster in water than in air, the dolphin&aposs brain must be extremely well adapted in order to make a rapid analysis of the complicated information provided by the echoes. Although the ability to echolocate has only been proven experimentally for a few odontocete species, the anatomical evidence - the presence of the melon, nasal sacs and specialized skull structures - suggests that all dolphins have this ability. The dolphin is able to generate sound in the form of clicks, within its nasal sacs, situated behind the melon. The frequency of this click is higher than that of the sounds used for communication and differs between species. The melon acts as a lens which focuses the sound into a narrow beam that is projected in front of the animal. When the sound strikes an object, some of the energy of the soundwave is rlected back towards the dolphin. It would appear that the panbone in the dolphin&aposs lower jaw receives the echo, and the fatty tissue behind it transmits the sound to the middle ear and thence to the brain. It has recently been suggested that the teeth of the dolphin, and the mandibular nerve that runs through the jawbone may transmit additional information to the dolphin&aposs brain. As soon as an echo is received, the dolphin generates another click. The time lapse between click and echo enables the dolphin to evaluate the distance between it and the object; the varying strength of the signal as it is received on the two sides of the dolphin&aposs head enable it to evaluate direction. By continuously emitting clicks and receiving echoes in this way, the dolphin can track objects and home in on them. The echolocation system of the dolphin is extremely sensitive and complex. Using only its acoustic senses, a bottlenose dolphin can discriminate between practically identical objects which differ by ten per cent or less in volume or surface area. It can do this in a noisy environment, can whistle and echolocate at the same time, and echolocate on near and distant targets simultaneously - feats which leave human sonar experts gasping.