首页
登录
职称英语
The majority of small tooth whales are called dolphins. Most dolphin species
The majority of small tooth whales are called dolphins. Most dolphin species
游客
2024-02-17
47
管理
问题
The majority of small tooth whales are called dolphins. Most dolphin species are about 6 ft in length, the males averaging 4 to 8 in. longer than females. The largest is the killer whale, which can be
ft long and weigh between 8000—10000 lbs. The smallest species is the buffeo, found in the Amazon River. The buffeo rarely grows over 3.9 ft in length and 66 lbs in weight.
Dolphins once were hunted commercially, especially for the small quantity of valuable oil extracted from palls of the head and used to lubricate delicate watch mechanisms. Cheaper oils have now been found from other sources, and dolphins are no longer hunted for this reason. Many dolphins, however, become accidentally trapped and drowned in tuna nets. Between the years 1959 and 1972, an estimated 4.8 million dolphins died this way. Because of the pressure from animal rights activists and the United States consumers, both domestic and international tuna canners have refused to accept shipments from fishing fleets that do not protect dolphins.
Dolphins are extremely and almost constantly vocal. They are capable of two kinds of sounds. A specialized mechanism in the nasal passage just below the blow-hole enables them to emit short, pulse-type sounds. These sounds, called clicks, can be produced in such rapid succession as to sound like a buzz or even a duck-like quack. The clicks are used as a form of sonar, in which echoes of sounds from surrounding objects enable the animals to detect obstacles, other dolphins, fish, and even tiny bits of matter in the water. The military use dolphins and this ability to help find water mines.
Deeper in the respiratory system-presumably in the larynx-dolphins produce another type of sound: a high pitched whistle of squeal, which is capable of rapid pitch changes. The whistles differ from the clicks in being essentially single tones. Apparently dolphins use the whistles to communicate a particular emotional state and thus influence the behaviour of other dolphins. Typically, the squeals denote alarm or sexual excitement. [br] The sound clicks differ from the squeals in that______.
选项
A、they are different in speeds of spreading
B、they are different in wave length
C、they are different in tones
D、they are different in volumes
答案
C
解析
转载请注明原文地址:http://tihaiku.com/zcyy/3458857.html
相关试题推荐
Researchershaveidentified1.4millionanimalspeciessofar—andmillions
Researchershaveidentified1.4millionanimalspeciessofar—andmillions
Researchershaveidentified1.4millionanimalspeciessofar—andmillions
Researchershaveidentified1.4millionanimalspeciessofar—andmillions
Researchershaveidentified1.4millionanimalspeciessofar—andmillions
Researchershaveidentified1.4millionanimalspeciessofar—andmillions
[originaltext]In1967,AmericanVoguemagazinepublishedanarticlecalled
[originaltext]In1967,AmericanVoguemagazinepublishedanarticlecalled
CaliforniahasanewprogramcalledtheDigitalTextbookInitiative."Starti
Topuniversitieshavebeencalledontopublishlistsof"banned"A-levelsu
随机试题
JardenZincProducts,alargezincplantafewmilesoutsideGreeneville,Ten
[originaltext]TheU.S.lawmakerswitnessedinterrogations,touredcellblocks
Intheolddays,childrenwerefamiliarwithbirthanddeathaspartoflife.
应与小儿腹股沟斜疝鉴别的疾病有A.睾丸鞘膜积液 B.睾丸下降不全 C.上述疾
在腹部闭合性损伤行手术治疗时,如未找到明确损伤,应进行探查的顺序A.肝、脾→胃→
脊柱骨折的形态,多属于A.裂缝骨折 B.线形骨折 C.压缩骨折 D.斜形骨
投资完成额的构成包括()。A.建筑工程 B.安装工程 C.设备、工具、器具购
吴茱萸除散寒止痛、燥湿止泻外,又能A.疏肝下气 B.温肺化饮 C.回阳救逆
根据《建筑工程施工质量验收统一标准》,符合专业验收规范规定适当调整试验数量的实施
采用氨为制冷剂的冷凝法回收含苯、甲苯、正己烷、乙二醇废气中的有机物,其回收设施尾
最新回复
(
0
)