标题: OG 13 CR 57有疑问，求指教 [打印本页] 作者: mslancaster 时间: 2012-12-28 07:03 标题: OG 13 CR 57有疑问，求指教
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？
