Question

【题目】Directions: Fill in each blank with a proper word chosen from the box. Each word can be used only once. Note that there is one word more than you need.

To many of us, the bilateral symmetry（左右对称） that characterizes the human face and the animal kingdom may be one of the first impressions we get of the world. If you reflect the left half of the face or body in a mirror, you obtain something that closely 【1】 the right half. Bilateral symmetry is so common that it could 【2】 be due to chance. If you think of the human body as a collection of some ten thousand trillion molecules, then there are countless ways to combine them into non-symmetrical shapes than into symmetrical ones. Why is it, then, that bilateral symmetry is so common? Given that all life on Earth slowly 【3】 through natural selection, the fact that we and many animals possess left-right symmetry, not, say, up-down or front-back symmetry, must have somehow 【4】 certain advantages. But how?

We can understand at least some parts of this natural “engineering” 【5】 by considering some simple physical principles. First, on the surface of the Earth, the Earth’s gravity introduces a 【6】 difference between up and down. Animals had to be able to remain stable and to cope with their weight under Earth’s perpetual downward pull. The ability to move further enhanced the difference between top and bottom.On one hand, birds had to handle the aerodynamics of flying, and on the other, be able to handle landing. Land animals had to develop some “mechanical” appendages (in other words, legs) to allow them to 【7】 themselves efficiently.

Animal locomotion was probably also 【8】 for the front-back asymmetry. Whether it was a bird, or a fish, having the sensory organs and the mouth in the front could mean the difference between finding lunch or missing it. The digestive and reproductive systems were pushed to the rear. Having eyes, ears, and noses in the front was also 【9】 for the avoidance of predators, and for the ability to explore an area before actually entering it. Life 【10】 that are fixed in one place or that move very slowly, such as trees or jellyfish, tend to have a different kind of symmetry, similar to that of a cone(球果) — they produce similar reflections in any mirror passing through their central axis.

Answer 1

【答案】

【1】D

【2】J

【3】C

【4】E

【5】K

【6】F

【7】B

【8】I

【9】H

【10】G

【解析】

这是一篇说明为。文章介绍了人类与动物在对称上的区别。对大多数人来说人类面部和动物王国的对称特征可能是我们对世界的第一印象之一。我们和许多动物都具有左右对称的特征，而不是上下对称或前后对称，这一事实在某种程度上赋予了我们某些优势。

【1】考查一般现在时态。句意：如果你把脸或身体的左半边反射到镜子里，你就得到了与右半部分非常相似的东西。结合句意可知此处用动词resemble“类似，想象”，再根据句子用一般现在时态，something是先行词，所以谓语动词用第三人称单数形式，故填D。

【2】考查副词。句意：左右对称是如此普遍，以至于它几乎不可能是偶然的。此处hardly“几乎不”是副词，修饰整个句子，符合句意。故选J。

【3】考查动词时态。句意：既然地球上所有的生命都是通过自然选择慢慢进化而来的，那么我们和许多动物都具有左右对称的特征，而不是上下对称或前后对称，这一事实一定在某种程度上赋予了我们某些优势。此处evolve“进化”是动词，句子用一般过去时态evolved，符合句意。故选C。

【4】考查情态动词must have done的用法。句意：既然地球上所有的生命都是通过自然选择慢慢进化而来的，那么我们和许多动物都具有左右对称的特征，而不是上下对称或前后对称，这一事实一定在某种程度上赋予了我们某些优势。此处是must have done结构，表示对过去事情有把握的肯定推测，grant“授予”是动词，用过去分词的形式granted，符合句意。故选E。

【5】考查名词。句意：通过考虑一些简单的物理原理，我们至少可以理解这个自然“工程”之谜的某些部分。此处puzzle“谜，难题”为名词，符合句意。故选K。

【6】考查形容词。句意：在地球表面，地球的重力在上下之间产生了明显的差异。此处是形容词作前置定语，修饰difference。marked“明显的”符合句意。故选F。

【7】考查动词不定式。句意：陆地动物必须发展出一些“机械”附属物(换句话说，腿)来让它们有效地移动自己。固定搭配allow sb. to do sth.“允许某人做某事”。此处transport“运输，流放”，是动词，作宾语补足语，符合句意。故选B。

【8】考查固定词组。句意：动物的运动也可能是造成前后不对称的原因。固定词组：be responsible for“对…负责”。符合句意。故选I。

【9】考查形容词。句意：在前面有眼睛、耳朵和鼻子也是躲避捕食者的关键，也是在进入一个区域之前进行探索的能力的关键。此处crucial“重要的，决定性的”是形容词，作表语，be crucial for“对…是重要的”。符合句意。故选H。

【10】考查名词复数。句意：固定在一个地方或移动非常缓慢的生命形式，如树木或水母，往往有一种不同的对称性，类似于圆锥体——它们在通过其中轴的任何镜子中产生类似的反射。此处form“形式”，是名词，和life forms一起构成句子的主语，故选G。