The safety of ships at sea does not depend only on the arrangements made in the ships themselves. Dangerous coasts and rocks may

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问题     The safety of ships at sea does not depend only on the arrangements made in the ships themselves. Dangerous coasts and rocks may be seen in the daytime,【C1】______they are a threat to safe navigation at night. Lighthouses are therefore erected at such places to【C2】______sailors of the danger. Modern lighthouses are put up at all dangerous places near the courses【C3】______by ships. On some rocky coasts several lighthouses may be built not far from each other, and【C4】______the sailors on a ship may know which is which, they have【C5】______arrangements of lights. One lighthouse will give a single flash at regular【C6】______, another may give two flashes; a third may give two followed by one; and so on. 【C7】______watching the lights the navigator is able to decide exactly where he is, and he can set his 【C8】______with confidence. In the approaches to some ports two continuous lights are set up, one above【C9】______but some distance behind; when they appear from the sea one above the other, the ship is on the right course; but if they do not, the captain knows that he is【C10】______his course and likely to strike a rock or the bottom of the sea.
【C6】

选项 A、distances
B、gaps
C、intervals
D、length

答案C

解析 A项distances指“距离”,在与介词at搭配时通常是at a distance of…“在……的距离处”,但不能用于at distances,也不与regular搭配,因此A项不正确。B项gaps意为“间隔,间隙”,不能与at搭配。D项length意为“长,长度”,at length是习语,意为“最后,终于”,但length也不能与regular搭配。因此只有C项intervals合适,是正确答案。interval意为“间隔”,at intervals意为“不时;每隔……时间”。本句中的at regular intervals指“定期”。
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