太奇“每日一练”:MPAcc英语阅读理解精篇(12.3)
4. Ocean exploration is not so expensive as space travel mainly because .
A) it is not affected by Earth's gravity
B) most undersea vehicles operate at the end of long ropes
C) ROVs have been put to use
D) There is no need for submersibles to get away from Earth's gravity
5. Which of the following is NOT MENTIONED in the passage?
A) New techniques are continually developed and new machines invented for undersea exploration
B) If not well built, a submersible is most likely to get crushed in deep water.
C) A submersible, when manned, looks very much like a spaceship.
D) In certain aspects undersea exploration is often faced with the same problem as space travel is.
参考答案:A B D D C
像太空探险领域一样,海底探险领域的新技术不断涌现。太空旅行和海洋探险二者既有很多共性,同时也有重大差异。
像宇宙飞船一样,载人潜水器必须在非自然环境中维持生存条件。在太空的真空状态下,宇宙飞船必须做到密封,而处于深海压力中的潜艇要能承载极大压力,否则会被挤压成碎片。太空探险领域,无人飞船先于载人飞船升空,而在海洋探险领域载人潜艇先于无人潜艇潜入海底,无人遥控潜艇最近才投入应用。真空是无线电通信的理想媒介,但水下通信仅限于很短的声波,这样,多数潜水器运行时都要拖着长长的电缆。
由于同样的原因,水下定位也比太空定位困难的多。对宇宙飞船的定位可以通过跟踪无线电信号完成,也可以借助望远镜或雷达完成。然而,对海底探险来说,必须要事先将专用的声纳系统放置在潜水区域才能完成对潜艇的定位。
尽管海洋探险在很多方面比太空探险有更多的要求,但是海洋探险自身有明显的优点:潜入海底不需要外力摆脱地球引力。因而海洋探险要廉价的多。