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The passage suggests which of the following about the accuracy of the commuter diatom’s biological clock?

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According to the passage, the periodic behavior displayed by commuter diatoms under constant laboratory conditions is characterized by which of the following?

以下是引用LES在2004-8-24 18:15:00的发言：

这两题完全没概念的说！

Q25 to Q28:

Recently biologists have been

interested in a tide-associated

periodic behavior displayed by

Line the diatom Hantzschia virgata, a

(5) microscopic golden-brown alga that

inhabits that portion of a shoreline

washed by tides (the intertidal zone).

Diatoms of this species, sometimes

called “commuter” diatoms, remain

(10) burrowed in the sand during high

tide, and emerge on the sand sur-

face during the daytime low tide.

Just before the sand is inundated by

the rising tide, the diatoms burrow

(15) again. Some scientists hypothesize

that commuter diatoms know that it

is low tide because they sense an

environmental change, such as an

alteration in temperature or a change

(20) in pressure caused by tidal move-

ment. However, when diatoms are

observed under constant conditions

in a laboratory, they still display

periodic behavior, continuing to bur-

(25) row on schedule for several weeks.

This indicates that commuter diatoms,

rather than relying on environmental

cues to keep time, possess an inter-

nal pacemaker or biological clock

(30) that enables them to anticipate peri-

odic changes in the environment.

A commuter diatom has an unusu-

ally accurate biological clock, a

consequence of the unrelenting

(35) environmental pressures to which

it is subjected; any diatoms that do

not burrow before the tide arrives

are washed away.

This is not to suggest that the

(40) period of this biological clock is

immutably fixed. Biologists have

concluded that even though a

diatom does not rely on the envi-

ronment to keep time, environmental

(45) factors—including changes in the

tide’s hydrostatic pressure, salin-

ity, mechanical agitation, and

temperature—can alter the period

of its biological clock according to

(50) changes in the tidal cycle. In short,

the relation between an organism’s

biological clock and its environment

is similar to that between a wristwatch

and its owner: the owner cannot

(55) make the watch run faster or slower,

but can reset the hands. However,

this relation is complicated in intertidal

dwellers such as commuter diatoms

by the fact that these organisms are

(60) exposed to the solar-day cycle as

well as to the tidal cycle, and some-

times display both solar-day and

tidal periods in a single behavior.

Commuter diatoms, for example,

(65) emerge only during those low tides

that occur during the day.

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Q25:

The passage suggests which of the following about the accuracy of the commuter diatom’s biological clock?

The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle.

The unusual accuracy that characterizes the commuter diatom’s biological clock is rare among intertidal species.

The commuter diatom’s biological clock is likely to be more accurate than the biological clock of a species that is subject to less intense environmental pressures.

The commuter diatom’s biological clock tends to be more accurate than the biological clocks of most other species because of the consistency of the tidal cycle.

The accuracy of the commuter diatom’s biological clock tends to fluctuate when the diatom is observed under variable laboratory conditions.

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Q27:

According to the passage, the periodic behavior displayed by commuter diatoms under constant laboratory conditions is characterized by which of the following?

Greater unpredictability than the corresponding behavior under natural conditions

A consistent periodic schedule in the short term

No difference over the long term from the corresponding behavior under natural conditions

Initial variability caused by the constant conditions of the laboratory

Greater sensitivity to environmental factors than is the case under natural conditions

GWD-1-Q28:

答案E，本帅不敢苟同！E生物钟的effectiveness 受到environmental factors 限制，显然不是。effectiveness 是说发挥的正常不正常。

28题答案是D，但我选A，关于生物钟，我在文中只找到biological infulences，实在没看到关于environmental influences 。郁闷中，请赐教。

以下是引用ggjen在2004-12-5 13:32:00的发言：
我打错了！！！应该是倒过来说，是我在文中只找到environmental influences ，实在没看到关于biological infulences。

A commuter diatom has an unusu-
ally accurate biological clock, a
consequence of the unrelenting
(35) environmental pressures to which
it is subjected; any diatoms that do
not burrow before the tide arrives
are washed away.
我觉得这个是25题的答案所在

而27题不可能是C，整个第二段都是在说时间长了，他们会受影响

This is not to suggest that the
(40) period of this biological clock is
immutably fixed

无情的环境压力致使diatom有一个不同寻常的准确的生物钟。.由此推出了没有这种重大压力的种类就不会有如此准确的生物钟。

A means, the accuracy of the commuter diatom's biological clock varies (by itself) according to changes in the tidal cycle.

B. The unusual accuracy that characterizes the commuter diatom’s biological clock is rare among intertidal species.

C. The commuter diatom’s biological clock is likely to be more accurate than the biological clock of a species that is subject to less intense environmental pressures.

赞成，several weeks确实存在很大的干扰，单独定位line21的话似乎缺乏说服力，只能再联系line 41的内容加以判断。

我也选了A，但在看以上讨论的时候，特别是26楼。我突然发现一个问题。

A:The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle.

我觉得A的句子主干是红色部分，但准确性改变（主动）与文章意思不一至。文章是说

can alter the period of its biological clock according to changes in the tidal cycle

因为把diatom拿到实验室的目的就是为了看看是否把环境压力消除了，它还能继续做周期性运动，所以C说在这两个环境是没有区别的。而B说它的行为是consistent的，可是从这个实验没有说它的行为是一直不变的。

而且短期长期在这个语境下是分辨不出来的，所以他们都没有错。