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  3. As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similari

As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similari

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问题 As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similarities with each other—as well as some important differences.
Manned submersibles.(潜水器), like spaceships, must maintain living conditions in an unnatural environment. But while a spaceship must simply be sealed against the vacuum of space, a submersible must be able to bear extreme pressure if it is not to break up in deep water.
    In exploring space, unmanned vehicles were employed before astronauts. In undersea exploration, on the other haled, men paved (铺路) the way, and only recently have unmanned remote-operated vehicles (ROVs) been put to use.
    One reason for this is that communicating with vehicles in orbit is much easier than talking to those underwater. A vacuum is an ideal medium for radio communications, but underwater communications are limited to much slower sound waves. Thus, most undersea vehicles—particularly ROVs—operate. at the end of long process.
    For a similar reason, knowing where you are undersea is much more difficult than in space. A spaceship’s position can be located by following its radio signal, or by using telescopes and radar. For an undersea vehicle, however, a special network of sonar (声纳) devices most be laid out in advance on the ocean floor in the area of a dive to locate the vehicle’s position.
    Though undersea exploration is more challenging than outer space in a number of respects, it has a distinct advantage: Going to the ocean doesn’t require the power necessary to escape Earth’s gravity. Thus, it remains far less expensive.
Which of the following is NOT mentioned in the passage?
选项 A、New techniques are continually developed and new machines invented for undersea exploration
B、If not well built, a submersible is likely to get crushed in deep water.
C、A submersible, when manned, looks very much like a spaceship.
D、In certain respects, undersea exploration is often faced with the same problem as space travel is.
答案C
解析 在第一段第1句中提到了A)项：正如在航天领域里一样，在海底探测方面也不断有新的技术出现, 第三段讲的实际上也是采用一个新技术的例子：在对海底的探索中，最先是靠潜水员，最近则采用了无人驾驶的遥控装置, B)项也提到了，见第二段第2句：潜水器必须能够承受极大的压力才不至于在深水中被压破, 第一段第2句说空间技术和海底探测技术有一些地方不同，也有许多相似的地方，接着第二段又说潜水器与宇宙飞船都需要保持非自然状态下的生活环境，这是两类技术有相似之处的例证, D)项在文中也有提及
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