Our ape-men forefathers had no obvious natural weapons in the struggle(1)_____ survival in the open. They had neither the powerf

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问题     Our ape-men forefathers had no obvious natural weapons in the struggle(1)_____ survival in the open. They had neither the powerful teeth nor the strong claws of the big cats. They could not (2)_____ with the bear, whose strength, speed and claws(3)_____ an impressive "small-fire" weaponry. They could not even defend themselves (4)_____ running swiftly like the horses, zebras or small animals. If the ape-men had attempted to compete on those terms(5)_____, they would have been(6)_____ to failure and extinction. But they were(7)_____ with enormous concealed advantages of a kind not possessed by any of their competitors.
    In the search(8)_____ the pickings of the forest, the ape-men had(9)_____ 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 permitted the ape-men to study practical problems(10)_____ that lay far (11)_____ the reach of the original inhabitants of the grassland. Good long-distance sight was(12)_____ another matter.
    Lack 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(13)_____ they had had to do was climb a tree. Out in the open, however, this simple solution was not(14)_____. Climbing a hill would have helped, but in many places the ground was(15)______. The ape-men(16)_____ 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(17)_____. It was extremely unstable and it meant that the already slow ape-men became slower still.(18)_____, they persevered and their bone structure gradually became(19)_____ to the new, unstable position that(20)_____ them the name Homo Erectus, upright man.
(5)

选项 A、in the open
B、in open
C、at the open
D、at open

答案A

解析 in the open为固定短语,表示“在露天”。从文章首句及第三段第二句也可找到该词组。
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