Our ape-men forefathers had no obvious natural weapons in the struggle for【C1】______in the open. They had neither the powerful teeth nor the strong claws of the big cats. They could not 【C2】______with the bear, whose strength, speed and claws【C3】______an impressive "small-fire" weaponry. They could not even defend themselves【C4】______running swiftly like the horses, zebras or small animals. If the ape-men had attempted to【C5】______on those terms in the open, they would have been【C6】______to failure and extinction. But they were【C7】______with enormous concealed advantages of a kind not possessed by any of their competitors. In the【C8】______for the pickings of the forest, the ape-men had【C9】______efficient stereoscopic vision and a sense of colour that the animals of the grasslands did not possess. The ability to see clearly at close range 【C10】______the ape-men to study practical problems in a way that lay far 【C11】______the reach of the original inhabitants of the grassland. Good long-distance sight was quite another matter. 【C12】______of long-distance vision had not been a problem for forest-dwelling apes and monkeys because the higher the viewpoint, the greater the range of sight—so【C13】______they had had to do was climb a tree. Out in the open, however, this simple solution was not【C14】______. Climbing a hill would have helped, 【C15】______ in many places the ground was flat. The ape-men【C16】______the only possible solution. They reared up as high as possible on their hind limbs and began to walk upright. This vital change of physical position brought about considerable【C17】______. It was extremely unstable and it meant that the already slow ape-men became slower still. 【C18】______, they persevered and their bone structure gradually became【C19】______ to the new, unstable position that【C20】______them the name Homo Erectus, upright man.

【正确答案】 A

【答案解析】解析：those terms指代前面将猿人和其他动物进行对比的几个方面——爪牙的坚固和锋利程度、体格的强壮程度、身手的敏捷度、奔跑速度等，对比的结果是，猿人在这些方面都不如其他动物厉害，若他们试图在这几方面与其他动物比拼的话，势必要落败；A项compete“竞争，较量，比试”代入此空，符合推断且语义通顺，故为本题答案。

【正确答案】 A

【答案解析】解析：空格所在句的大意为“在_____森林中可以采摘的东西的过程中，猿人______良好的立体视觉和色感”，虽然本句还有下一空没填，但结合下文的内容推测，此处应该是讲猿人在视觉方面拥有的区别于其他动物的优势，A项search“搜寻，寻找，寻求”代入此空，表示“在寻找森林中可以采摘的东西的过程中”，与上下文语义逻辑相符，故本题选A。

【正确答案】 C

【答案解析】解析：结合下文的内容(The ability to see clearly at close range．．．)推测，此处应该是讲猿人在视觉方面拥有的区别于其他动物的优势，空格后接“立体视觉和色感”，developed能表示“自身潜在技能的开发”，而“立体视觉和色感”属于一种自身潜能，搭配合适，代入后表示“猿人逐渐具备了良好的立体视觉和色感”，与上下文语义衔接通顺合理，故本题选C。

【正确答案】 A

【答案解析】解析：此空所在句大意为“可以看清近距离的物体的这种能力_______猿人以一种……方式来考虑实际问题”，从句意上看，A项permitted“允许，使有可能”符合要求，permit sb．to do sth．表示“允许某人做某事，使某人得以做某事”，句意通顺，逻辑合理，故A为本题答案。

【正确答案】 B

【答案解析】解析：上一段主要讲猿人在视觉上的优势——能看清近距离的事物，末句则说“良好的远程视力则完全是另一回事了”。注意这里用了quite another matter，言下之意，猿人在远视能力方面应该跟其短距离视力优势相去甚远，甚至是另一个极端，即有可能是完全不具有远视能力。而此空所在句说远视能力方面的问题，居住在森林的猿猴可以通过(爬树)提高视点从而扩宽视野来解决。根据此处的上下文，可以推测猿人应该不具备远视能力，因此选B项Lack“缺乏，没有”。