Tracking whales is but one example of an exciting new world just opening to civilian scientists after the cold war as the Navy starts to share and partly uncover its global network of underwater listening system built over the decades to track the ships of potential enemies.

　　Earth scientists announced at a news conference recently that they had used the system for closely monitoring a deep-sea volcanic eruption (爆发)for the first time and that they plan similar studies.

　　Other scientists have proposed to use the network for tracking ocean currents and measuring changes in ocean and global temperatures.

　　The speed of sound in water is roughly one mile a secondslower than through land but faster than through air. What is most important, different layers of ocean water can act as channels for sounds, focusing them in the same way a stethoscope (听诊器)does when it carries faint noises from a patients chest to a doctors ear. This focusing is the main reason that even relatively weak sounds in the ocean, especially low-frequency ones, can often travel thousands of miles.

　　31.The passage is chiefly about ________.

　　A) an effort to protect an endangered marine species

　　B) the civilian use of a military detection system

　　C) the exposure of a U. S. Navy top-secret weapon

　　D) a new way to look into the behavior of blue whales

【2012年12月英语四级阅读备考：全真试题(7)】相关文章：

★ 英语四级阅读全攻略：细节题解题思路

★ 2013年12月英语六级改革的模拟练习长篇阅读4

★ 英语四级快速阅读攻略：略读和跳读配合

★ 英语四级考试阅读备考材料(3)

★ 2010年6月英语六级考试的标准阅读第14篇

★ 2014年12月英语六级阅读理解真题训练：Happiness

★ 2007年12月英语六级考试阅读冲刺的模拟训练7

★ 2012年12月暑期英语六级备考阅读每日一练 0813

★ 2011年最新六级阅读理解练习（21）

★ 2013年12月六级外国期刊双语阅读：学生的压力