OG12-59

Hyozia

In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles fromclinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?

(A)Tidal currents donot themselves dislodge barnacles from the shells of horseshoe crabs.

(B)Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.

(C)The strength of the tidal currents in a given location varies widely over the course of a day.

(D)A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.

(E)Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.
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OA---E
粗略分析：1.未成年的马蹄蟹经常埋在沙子里以抵抗潮汐  2.埋到沙子里就阻止了B附着在螃蟹壳上 3.成年蟹有足够力量不用埋起来了，因此上面应该附着大量的B 4.奇怪的是，在潮汐非常弱的地区，马蹄蟹在不埋起来的情况下也没有被大量的B附着。这里2和4构成了paradox，意思是说按1和2，幼年的蟹在潮汐非常弱的地区不用埋起来，应该会附着大量的B，但是4说没有附着，由此选E
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但是，这样看题目仍有无法解释的东西：既然选了E，那么如何解释在潮汐弱的地区，成年蟹身上也没有B附着呢？？？？

sdcar2010

LZ, read carefully the last sentence:

juvenile horseshoe crabs are found not to have significant barnacle populations. Juvenile is not adult.

Hyozia

..................sorry, my poor vocabulary~~~~~

米样

我还有一种解释，不知道大家觉得对不对？
A.大浪—小马蹄蟹打洞—没有b；
B.大马蹄蟹不打洞—大量b；
C.surprising：微浪—小马蹄蟹不打洞——没有b。
A和C相比较，发现：有没有b和浪的大小、是否打洞，没有关系；
B和C相比较，发现：有没有浪和马蹄蟹的大小有关系，也就是说区别在于juvenile 和 fully grown

看选项，A B C 都在说浪，一看就排除了；D项无关；只有E项提到了 fully grown，就是它了！！!

引夕

我想问为什么D不可以= =………不能理解为因为barnacle会降低crab找食物的能力所以有大量barnacle的crab都死了只剩有少量的了…………？

liweijz

樓上，不能那麼推理。
1 D項和conclusion沒有直接的關係
2 降低找食物的能力不一定可以推出crab會死。