首页
登录
职称英语
Comparatively few fresh-water species of fishes are limited in their distrib
Comparatively few fresh-water species of fishes are limited in their distrib
游客
2023-07-04
36
管理
问题
Comparatively few fresh-water species of fishes are limited in their distribution to a single river system, yet not many are found on both sides of a high mountain ridge, such as the Rocky Mountains in North America. That is to say, the fishes of the Mississippi Valley are generally different from those of the Pacific slope.
While it is a well-known fact that the fish life in no two river systems, even though they empty into the sea on the same side of a divide(分水岭), is exactly identical, such streams do have many species in common. The principal rivers of the Atlantic slope of the United States, for example, contain several species common to all of them, including the bullhead catfish, the bluegill sunfish, and the largemouth bass. None of these species can endure salt water, so they cannot move from one river system to another. On the other hand, the more northern streams contain species not found in the southern ones, and vice versa. The common pike, for example, is found in the Atlantic streams from Maryland northward, and the brook trout and yellow perch occur only in the streams from North Carolina southward.
How the present distribution came about must remain a matter of guess. It is quite probable that some of the streams, including those on opposite sides of a divide, may have been connected at one time. Again, streams may be entirely separate during normal weather, but an exceptionally heavy rainfall or the sudden melting of snow in the uplands sometimes causes floods which may form a temporary connection between them, providing a passageway for fishes. It is also possible that water birds may accidentally carry fish or spawn(卵)from one stream to another, or that man may be instrumental in such a transfer.
Evidently, then, fresh-water fishes may become distributed far beyond the confines of the stream of their origin. Then chief factor in limiting the still wider distribution of species is temperature. This forms such an efficient barrier that comparatively few species of fresh-water fishes of the United States extend their range into Mexico. In Panama only one fish common to the fresh waters of the United States has been found, and that is the eel, which is not strictly a fresh-water form, as it enters salt water to spawn and is taken in fairly salty water at other times. [br] The fishes in the Atlantic slope cannot move from one river system to another because______.
选项
A、there is no canal linking different rivers
B、fishes cannot swim by way of the Atlantic
C、different rivers do not have the same salt content
D、different fishes need different rivers
答案
C
解析
推理题。第二段第三句指出Atlantic Slope里的鱼都无法忍受咸水,所以它们无法从一条河迁徙到其它的河。也就是说明每条河的含盐量都是不同的。
转载请注明原文地址:https://tihaiku.com/zcyy/2807016.html
相关试题推荐
Aleadingbiologisthascomparedthephysiology(生理学)offlightedspecieswith
Aleadingbiologisthascomparedthephysiology(生理学)offlightedspecieswith
Aleadingbiologisthascomparedthephysiology(生理学)offlightedspecieswith
Aleadingbiologisthascomparedthephysiology(生理学)offlightedspecieswith
Aleadingbiologisthascomparedthephysiology(生理学)offlightedspecieswith
TheEarthhasbeenstrippedofupto90%ofitsspeciesfivetimesbeforein
TheEarthhasbeenstrippedofupto90%ofitsspeciesfivetimesbeforein
TheEarthhasbeenstrippedofupto90%ofitsspeciesfivetimesbeforein
TheEarthhasbeenstrippedofupto90%ofitsspeciesfivetimesbeforein
TheEarthhasbeenstrippedofupto90%ofitsspeciesfivetimesbeforein
随机试题
[originaltext]Fivemillionjobsintheworld’sleadingeconomiescoulddisa
Accordingtothepassage,ifallstudentsattendyear-roundschoolsinU.S.they
Twogroupsofscientistsdemonstratedlastweekfoxthefirsttimethatthe
ArecentBBCdocumentary,TheTownThatNeverRetired,soughttoshowtheef
如图所示,一滑块从半圆形光滑轨道上端由静止滑下,当滑到最低点时,关于滑块动能大小
2008年7月,中国证监会发布实施了《证券公司合规管理试行规定》,证券公司应设立
心跳骤停后最容易发生的继发性病理变化是()。A.肺水肿 B.急性肾衰竭 C
下列关于我国城镇职工基本医疗保险(简称职工医保)的说法正确的是:A.灵活就业人群
一天中人体生长激素水平最高的时段是 A.清晨B.中午C.快波睡眠D.慢波
下面是某求助者的EPQ测验结果: ?多选:该求助者各维度得分低于常
最新回复
(
0
)