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标题: Prep1-24 [打印本页]

作者: lzhang7705 时间: 2009-10-7 23:19
标题: Prep1-24

好像站内没有关于这道题目的讨论。哪位同学帮忙看看。答案是C, 可我不太明白啊！谢谢

24. (29155-!-item-!-188;#058&003857)

Tiger beetles are such fast runners that they can capture virtually any nonflying insect. However, when running toward an insect, the beetles intermittently stop, and then, a moment later, resume their attack. Perhaps they cannot maintain their pace and must pause for a moment's rest; but an alternative hypothesis is that while running tiger beetles are unable to process the resulting rapidly changing visual information, and so quickly go blind and stop.

Which of the following, if discovered in experiments using artificially moved prey insects, would support one of the two hypotheses and undermine the other?

(A) When a prey insect is moved directly toward a beetle that has been chasing it, the beetle immediately turns and runs away without its usual intermittent stopping.

(B) In pursuing a moving insect, the beetles usually respond immediately to changes in the insect's direction, and pause equally frequently whether the chase is up or down an incline.

(C) The beetles maintain a fixed time interval between pauses, although when an insect that had been stationary begins to flee, the beetle increases its speed after its next pause.

(D) If, when a beetle pauses, it has not gained on the insect it is pursuing, the beetle generally ends its pursuit.

(E) When an obstacle is suddenly introduced just in front of running beetles, the beetles sometimes stop immediately, but they never respond by running around the barrier.

作者: amumu 时间: 2009-10-25 21:59

The beetles maintain a fixed time interval between pauses, although when an insect that had been stationary begins to flee -> weaken latter

the beetle increases its speed after its next pause. -> support former

作者: FFcapm 时间: 2009-10-25 23:57
still not sure...

anyone has more clear explanation?

作者: heygika 时间: 2009-11-16 22:04
I go with C..

support one hyp and undermine other.

TB fast runners can capture any non flying insect
running towards insect, int. stop and resume
Hyp 1 : cannot maintain their pace so pause for rest
Hyp 2 : cannot process rapidly changing visual info. go blind hence stop

A) When a prey insect is moved directly toward a beetle that has been chasing it, the beetle immediately turns and runs away without its usual intermittent stopping.

This sentence suggests a survival issue for Beetle. So whether or not it needs rest or become blind, it has to save its life so keep running. This is not the answer.

B) In pursuing a moving insect, the beetles usually respond immediately to changes in the insect's direction, and pause equally frequently whether the chase is up or down an incline.
"usually respond immediately to changes" implies beetle does not become blind so refuting the second hypothesis. "pause equally frequently whether..." implies irrespective of condition they stop, so "rest" is not the issue, as if it is an issue then going up incline they will rest more frequently.

C) The beetles maintain a fixed time interval between pauses, although when an insect that had been stationary begins to flee, the beetle increases its speed after the next pause.
"maintain a fixed time interval..." refutes first experiment. "though when an insect..." supports beetle is not able to see it when prey started fleeing, so next time when beetle pauses and see prey is fleeing increases its speed.

D) If, when the beetle pauses, it has not gained on the suspect while pursuing, the beetle generally ends the pursuit.
Neither supports the first hypothesis nor the second hypothesis.

E) When an obstacle is suddenly introduced just in front of the running beetles, the beetles stop immediately, but they never respond by running around the barrier.
"When an obstacle is.." indicates beetle is not blind thereby refuting second hypothesis but this does not supports the first experiment as required by the question.

So Answer is C.

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