OG 13 CR 57有疑问，求指教

维以不永伤6

In order to withstand tidal currents, juvenile horseshoe
crabs frequently burrow in the sand. Suchburrowing
discourages barnacles from clinging 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, eventhough they
seldom burrow.
Which of the following, iftrue, most helps to explain
the surprising finding?


(A) Tidal currents do not 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) Avery 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. （correct）



自己写的mind-map:
少HC withstand tide---burrow (降B to shells)/ 成年HC withstand--少HC not burrow(多B). BUT, no burrow, 不多 B. WHY?


A-D错误都明白，但是E正确有点看不明白，特别是后半句grow new ones several times 主语是HC吧，HCgrow有什么意义呢？


求指教，感激不尽！

嘿，小春虫虫

elinkwok 发表于 2012-10-9 23:57
我是这么想的: 就是说在那种crab完全长成熟之前他一直要脱落旧的壳, 换新的壳, 所以HC换壳的意义在于, 这样 ...

我在想如果是因为Crab换壳导致B少，那么在其它的地区的crab也会换壳啊，那么所有地方crab上的B都会少，而不会出现barnacles become more likely to cling to their shells的局面了啊？

维以不永伤6

明白了谢谢！

elinkwok

我是这么想的: 就是说在那种crab完全长成熟之前他一直要脱落旧的壳, 换新的壳, 所以HC换壳的意义在于, 这样就算cling在他们身上的barnacle也会随着被脱落的壳同时脱掉，所以populationi就没有很多.

注意文中说的是在currents很弱的地方的JUVENILE crabs没有很多b在他们身上. 所以用E选项就可以解释为因为他们一直再换壳, 所以新的壳不会有很多b.