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标题: 可否帮忙给出GWD一篇阅读的答案 [打印本页]

作者: zhangnannan 时间: 2006-11-17 23:49
标题: 可否帮忙给出GWD一篇阅读的答案

GWD11-Q24 to Q27:

Anole lizard species that

occur together (sympatrically)

on certain Caribbean islands

Line occupy different habitats:

(5) some live only in the grass,

some only on tree trunks, and

some only on twigs. These

species also differ morpho-

logically: grass dwellers are

(10) slender with long tails, tree

dwellers are stocky with long

legs, twig dwellers are slender

but stubby-legged. What is

striking about these lizards

(15) is not that coexisting species

differ in morphology and habi-

tat use (such differences are

common among closely related

sympatric species), but that

(20) the same three types of habi-

tat specialists occur on each

of four islands: Puerto Rico,

Cuba, Hispaniola, and Jamaica.

Moreover, the Puerto Rican

(25) twig species closely resembles

the twig species of Cuba,

Hispaniola, and Jamaica in

morphology, habitat use, and

behavior. Likewise, the spe-

(30) cialists for other habitats are

similar across the islands.

The presence of similar

species on different islands

could be variously explained.

(35)
An ancestral species might

have adapted to exploit a

particular ecological niche on

one island and then traveled

over water to colonize other

(40) islands. Or this ancestral

species might have evolved

at a time when the islands

were connected, which some

of these islands may once

(45) have been. After the islands

separated, the isolated lizard

populations would have become

distinct species while also

retaining their ancestors’ niche

(50) adaptations. Both of these

scenarios imply that speciali-

zation to each niche occurred

only once. Alternatively, each

specialist could have arisen

(55) independently on each of the

islands.

If each type of specialist

evolved just once, then similar

specialists on different islands

(60) would be closely related.

Conversely, if the specialists

evolved independently on each

island, then a specialist on one

island would be more closely

(65) related to other types of anoles

on the same island—regardless

of their ecological niches—

than it would be to a similar

specialist on a different island.

(70) Biologists can infer how

species are related evolu-

tionarily by comparing DNA

sequences for the same genes

in different species. Species

(75) with similar DNA sequences

for these genes are generally

more closely related to each

other than to species with less-

similar DNA sequences. DNA

(80) evidence concerning the anoles

led researchers to conclude

that habitat specialists on one

island are not closely related

to the same habitat specialists

(85) elsewhere, indicating that spe-

cialists evolved independently

on each island.

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GWD11-Q24 to Q27:

Q24:

The primary purpose of the passage is to

describe some unusual features of anole lizard species
account for a particular type of behavior found among anole lizard species
contrast two types of evidence that have been used to support a particular hypothesis concerning anole lizard species
explain how researchers resolved a particular scientific question concerning anole lizard species
examine different explanations for a particular trait common to certain anole lizard species

Answer:

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Q25:

Which of the following best describes the purpose of the sentence in lines 13-23 (“What is … Jamaica”)?

It raises a question about why coexisting anole lizard species occupy the different types of habitats mentioned in the first sentence.
It introduces a fact about anole lizard species that the passage will go on to explore.
It identifies a particular aspect of anole lizard behavior that distinguishes anoles from other lizard species.
It explains why one aspect of anole lizard species’ habitat use has been difficult to account for.
It points out a surprising relationship between morphology and habitat use that is explained in the concluding paragraph.

Answer:

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Q26:

It can be inferred form the passage that which of the following is true of the Cuban tree-dwelling anole lizard and the Jamaican tree-dwelling anole lizard?

They share a morphology characterized by stocky bodies and long legs.
They have bodies that are relatively slender compared to their stubby legs.
They differ significantly form one another in size.
They differ significantly from one another in behavior and habitat use.
They are genetically closely related to one another.

Answer:

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Q27:

The passage suggests that if a grass-dwelling anole lizard species evolved on one island and then traveled over water to colonize a second island, the grass-dwelling anoles on the two islands would eventually

develop very different DNA sequences
develop into different species that are more distantly related to each other than to tree- and twig-dwelling anoles on their own islands
come to differ significantly from one another in habitat use
develop into different, but closely related, species
evolve significant morphological differences

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