一題新的變形題

ai559031

Which of the following most logically completes the argument ?

Lyme disease is caused by a bacterium transmitted to people by deer ticks. Deer ticks are almost never born infected with the bacterium, but they can pick it up from feeding on an infected host in any of the tick's three successive stage of development: larva, nymph, adult. Once infected, a tick remains infected through any subsequent developmental stages, but since a tick feeds on only one host in each stage, it follows that ______________

A. People can be infected only by being bitten by a tick that is either in larval stage or in the nymph stage
B. People cannot be infected by a tick that picked up the Lyme disease bacterium in the adult stage
C. It is not possible for a person to be infected by a tick that is in the nymph stage or by a tick that was infected with the bacterium while in the nymph stage
D. People infected with the Lyme disease bacterium cannot transmit bacterium to adult deer ticks
E. Only deer ticks that are adults can transmit the Lyme disease bacterium to people

ans. B

不太懂Ｂ選項...然後Ｄ為什麼是錯的
感謝～～

容绮

原文的意思是说deer tick一生中有三个阶段，每个阶段只会feed on一个host.
所以B选项说的是人不会被一个在adult stage才被感染的deer tick传染。这个正确，因为tick在一个阶段只会feed on一个host, 所以在adult stage的话这个tick只会feed on这个使它感染的host，所以不会再去feed on其他人了。
D选项说人不能把bacterium传给adult stage的deer tick. 这个错误。一个感染了的人如果成了tick在adult stage 的唯一host，自然就把bacterium传给tick了。

希望能帮到楼主~~~

ai559031

容绮 发表于 2016-7-30 13:00
原文的意思是说deer tick一生中有三个阶段，每个阶段只会feed on一个host.
所以B选项说的是人不会被一个在a ...

喔喔！我懂了～
也就是說tick有三個階段，每個階段只能有一個host
所以在larva stage，他還有兩次機會可以 feed on an infected host
nymph stage還有一次
到了adult stage的時候，因為已經是最後一階段了，所以他被感染後，基於一個stage只能有一個host，所以答案選Ｂ
感謝～～

growing0424

感谢解析！这题看懵了好久啊  

Monica2020

看一下！               

Bensontuo

Spot the question type : Must be true

很明顯的答案

如果頭蝨在生命中的三個階段都只能有一個宿主, 而在最後的一個階段感染了疾病, 那就代表就是那個宿主讓頭蝨感染了這個疾病, 既然有了宿主, 頭蝨不會更換宿主, 既然不會更換宿主, 那人怎麼會被感染呢？

頭蝨一定要先叮咬宿主才可以得病, 而就算得病, 頭蝨也不會更換其他宿主, 就是跟你走一輩子的意思啦～

Ｄ, 不對啊, 沒有人說不可以有多隻頭蝨一起叮咬人類啊, 要是有一隻感染的頭蝨讓人類感染了, 而另外一隻頭蝨剛好在生命最後一個階段來叮咬這個人類, 那這隻頭蝨原本沒病, 不就有因為叮咬了被感染的人類所以有病了嗎？

Eres

感谢分享！               

tu-yu

感谢分享！               

skating_girl

这题令我感到迷惑的是，a和b难道 不是一个意思吗？
B说人不会在其处于adult的阶段被感染，而它又只存在三个阶段，所以不就是相当于在说A的只会在另外两个阶段L和N阶段被感染吗？

skating_girl

搬运一下：
OK .. trying to explain as simply as I can:

Deer ticks: an insect that has three phases (say I, II and III) in life. This insect is carrier of a bacteria (say X) that causes Lyme disease. The insect gets the bacteria X from someone else (say H1) while feeding on H1, who is already infected with the bacteria. Later the insect delivers the bacteria X to someone else (say H2) while feeding on H2.

The condition is that taking up and delivering of bacteria X cannot happen in the same phase of the insect's life because the insect feeds on only one animal or person in one phase of it's life (it cannot feed on both H1 and H2 in the same phase). If the insect gets the bacteria in phase I, it can deliver it in phase II or III. If the insect gets the bacteria in phase II, it can deliver it in phase III. If it gets in phase III, it cannot deliver at all.

Hosts: Hosts are the entities (could be humans or any animal) on whom the above insect feeds. H1 and H2 are both hosts (hosts of the insect).

Now read the explanations in the previous posts and hopefully you will understand the argument.