首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Choose the correct answer, A, B or C. What change caused changes in crocodile populations in North Africa?
Choose the correct answer, A, B or C. What change caused changes in crocodile populations in North Africa?
admin
2015-08-06
63
问题
Choose the correct answer, A, B or C.
What change caused changes in crocodile populations in North Africa?
Good morning! Today we will continue our study of Crocodylus niloticus by talking about its living habits. We’ve already discussed the evolutionary attributes that set it apart from its crocodile relatives. Does everyone remember that?
Yes, it has an extremely narrow snout, and three or four rows of protective scales on its back, as compared to two rows on other members of the Crocodylus genus.
Let’s take a look at how these carnivorous man-eaters live, where they live, and finally, whether they really deserve their vicious reputation.
To start, I’d like to address a great question posed to me by a student during yesterday’s office hours. We talked about the distribution of crocodiles in Africa and saw that they are highly concentrated in the South and West of the continent. This student noticed that on the map displaying the distribution of crocodiles across Africa, there were no crocodiles in the Northern Region, and found no mention in the literature of the existence of crocodiles in the North of Africa. Why might there be no crocodiles in North Africa? Let’s save this question for later in the lecture.
To find out more about the social habits of the African crocodile, one researcher named Tara Shine of the University of Ulster in Northern Ireland conducted a survey of the wetlands in Mauritania and received reports of 46 crocodiles living in one group, or float as we say when referring to crocodiles, though the usual number is a little less than half that.
In general, crocodiles are more highly concentrated in wet, sub-tropical environments near bodies of water and rich vegetation. While South American crocodiles thrive in cool rainforests, the African crocodile is more equipped for heat. Though they can survive at the hot temperatures found in some deserts, they are not equipped to handle dry climates and thus cannot survive in places like the Sahara Desert of North Africa. As cold-blooded animals, crocodiles’ core temperatures fluctuate from their average of 38 degrees Celsius as external conditions change, thus they need to avoid extreme temperatures. Others live an underwater life, keeping a body temperature close to that of the water. As their own unique method of regulating their body temperatures, some African crocodiles have made dens by digging holes in the ground to provide themselves with a cool, dark place to retreat from the hot African sun.
Speaking of the hot African sun, let’s go back to the question asked at the beginning of the lecture. We know that there used to be crocodiles in Northern Africa, yet today there are none. What are some possible explanations for this?
Some students have suggested that the African crocodile has evolved from a desert creature into a wetland creature, thus causing them to migrate south for more appropriate condition. Others presume that the crocodile was hunted out of Northern Africa by a fiercer predator. While these are intelligent guesses, the real story is a little bit different.
The key to this migration is that the Sahara Desert did not always cover the north of Africa. About 8,000 years ago, the land was fertile wetlands perfect for breeding crocodiles. Over time, though, the area dried out and the wetland slowly turned to desert, leading the African crocodile to migrate south to the marshlands they call home today.
Some crocodiles did, however, adapt to living in dry conditions. In Mauritania, some crocodiles have learned to survive in an area where they can go up to 8 months with no water by spending the driest of times in what’s called a torpor, or short period of hibernation. To utilise every bit of rainfall, these desert crocodiles dig underground caves that collect runoff, thus staying cool and hydrated.
During the mating period in November and December, males attract females to their viciously protected territory through a number of behaviors that range from snapping their jaws all the way to sending infrasonic pulses through the water. Afterwards the female digs a hole up to 60 cm in depth to store the eggs for an 80-day incubation period. The female protects these eggs during the period, and sometimes even helps crack the eggs with her snout at the end.
These teeth-gnashing carnivores are softer than we think. Although these vicious creatures have attacked humans on a few occasions, the residents are not afraid of them. In fact, they show a great deal of reverence toward these wondrous creatures. Some say that crocodiles bring water to their habitat, so if they leave, they will bring the water with them. Obviously this is not true, but it demonstrates the admiration the inhabiting people have for crocodiles.
Generally crocodiles do not predate on humans. They attack when humans populate the crocodiles’ habitat, instilling fear and uneasiness in the crocs. Like any other species, crocodiles are known to attack when feeling fear.
There’s still a lot more to be discovered about the African crocodile. Researchers want to know more about the population size - how many crocodiles inhabit Africa in all, how they form separate floats, etc.
There is still also much to learn about migration patterns, and relations to other populations of crocodiles now found in other parts of the world.
Next time we’ll examine a few specific case studies of crocodile populations in Southern Africa.
选项
A、They were driven away by a fierce predator.
B、Crocodiles evolved from desert creatures to wetland creatures.
C、North Africa used to be wetland but slowly turned to desert over time.
答案
C
解析
C本题题干与原文相比变化不大,原文:Over time,though,the area dried out and the wetland slowly turned to desert,leading the African crocodile to migrate south to the marshlands they call home today.与C选项相呼应。
转载请注明原文地址:https://kaotiyun.com/show/oOAO777K
本试题收录于:
雅思听力题库雅思(IELTS)分类
0
雅思听力
雅思(IELTS)
相关试题推荐
Whydidyouchoosethismajor?
Onwhatoccasionswouldpeoplegiveflowerstootherpeople?
WRITINGTASK2Youshouldspendabout40minutesonthistask.Writeaboutthefollowingtopic:Increasedmeasuresh
ThechartshowshouseholdsavingsasapercentageofincomeforpeoplelivinginHongKong.Summarisetheinformationbyselecti
Morethanfourdecadesago,manforthefirsttimesetfootonthemoon.Somepeoplethinkthatspaceresearchisawasteofene
Youareatenantandhaveunintentionallydamagedsomethingthatisthepropertyofthelandlord.Writealettertotheland
Questions27-30Foreachquestion,onlyONEofthechoicesiscorrect.Writethecorrespondingletterintheappropriateboxon
Questions28-29Completethenotes,whichshowhowtheapproachestodefining’talent’havechanged.ChooseONEorTWOWORDSfro
Questions28-29Completethenotes,whichshowhowtheapproachestodefining’talent’havechanged.ChooseONEorTWOWORDSfro
Questions28-29Completethenotes,whichshowhowtheapproachestodefining’talent’havechanged.ChooseONEorTWOWORDSfro
随机试题
下列与十进制数10.5相等的是
患者,男,65岁。因阵发性腹部绞痛5小时入院,腹痛发作时自觉有腹内气块窜动感,伴呕吐胃内容物多次,肛门有少量排气。腹部X线显示肠黏膜皱襞呈“鱼肋骨刺”状改变。该患者可能发生
心肌梗死的病人哪种同工酶明显升高
用尿糖定性试验检查糖尿病病人和正常成年人各500名,结果糖尿病病人中有300例阳性,200例阴性,正常成年人有50例阳性,450例阴性。尿糖定性试验筛检糖尿病的灵敏度为
集料的含泥量是指集料中粒径小于或等于()的尘宵、淤泥、粘土的总含量。
依据委托监理合同示范文本,当委托人严重拖欠监理酬金而又未提出任何书面解释时,监理人可()。
下列选项在金融市场中,既是金融市场中重要的交易主体,又是监管机构之一的是()。
划分就是把一个概念所反映的对象分为几小类来眀确概念外延的逻辑方法,也可以说是把一个外延较大的属概念分成几个并列的种概念的逻辑方法。分解是在思维中将一个对象分成几个部分,反映部分的概念和反映整体的概念之间不是种属关系。根据上述定义,下列属于正确划分的是:
在各类计算机操作系统中,分时系统是一种()。
Shortstoriesareduearevival.Inrecentyears,therehavebeencritically(1)_____collectionsbyAmericanwriterssuchasLyd
最新回复
(
0
)