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  3. Peahens, though not as showy as cocks, are by no means plain. Their heads have attractive crests and their necks are bright blue

Peahens, though not as showy as cocks, are by no means plain. Their heads have attractive crests and their necks are bright blue

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问题    Peahens, though not as showy as cocks, are by no means plain. Their heads have attractive crests and their necks are bright blue. Such decoration is costly to grow and likely to attract predators. If you do not have to show off your stuff to get a mate, why do you need it? Even more confusingly, in many species both sexes are equally showy. To understand things better James Dale of Massey University, in Auckland, New Zealand, and his colleagues have therefore examined the feathers of both sexes of all 5,983 species of passerine bird (雀形目鸟类) and compared them in exquisite detail. 【F1】The researchers started from the fact that, despite the exceptions, showiness is still more a male than a female phenomenon.
   【F2】Their first observation, as they report this week in Nature, was that in species where a few males exclusively control all the females, with a consequent lack of male involvement in parental care, males were more colourful than females. This is what the theory of sexual selection would predict. What it would not predict in its simple form, though, was a second finding—that females in co-operatively breeding species (those in which, for lack of other opportunities, several females collaborate to raise the young of only one of them) are more ornamented than those in which all adult females have a chance of breeding. 【F3】In this case it is females who are competing for the right to reproduce, thus putting themselves in a more male-like position.
   Another widespread belief Dr Dale and his colleagues confirmed is that tropical species are more colourful than those from temperate climes. But again, there was a twist—the effect was much more marked in females than in males. 【F4】It may be that tropical birds, which face more intense competition for food and nesting sites than temperate ones do because the tropics have more species, form more stable and collaborative pair-bonds than do temperate birds. In these circumstances males also need to be choosy, and females competitive.
   The final effect the researchers found was that big species are more colourful than small ones. That is true of both sexes, and probably reflects the fact that bigger birds are more difficult prey and thus have less need to hide. When released from the threat of predation, then, females tend to be showy. 【F5】That suggests showiness is always good when it can be got away with and probably explains the decorated necks and heads of peahens, which are among the biggest of birds.
【F5】
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答案这表明在无惧天敌威胁的情况下，外表华丽点总是好的，这或许也解释了为何雌孔雀拥有艳丽的脖子和冠，因为它是体型最大的鸟类之一。
解析 ①本句为多重复合句，主句主语That指代上一句When．．．，females tend to be showy；主句包含两套谓宾结构，其中第一个宾语由省略了引导词的从句充当，该宾语从句中还包含when引导的时间状语从句以限定showiness is always good的前提条件，即“在不受天敌威胁的情况下”。②逗号后which引导定语从句修饰先行词peahens，说明雌孔雀的体型特征，即“体型最大的鸟类之一”。
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