Language Points
1.Not all sounds made by animals serve as language, and we have only to turn to that extraordinary discovery of echo-location in bats to see a case in which the voice plays a strictly utilitarian role.
serve as : 作为，用作
例句：One room had to serve as both bedroom and living room.
一间屋子只能既作寝室又作起居室使用。
turn to : 求助于
例句：They had to turn to to the villagers for advice.
他们不得不向村民们求助。
play a role in ... 在 ...里面扮演角色，发挥作用
例句：She played the leading role in the school play.
她在学校的戏里扮演主角。
2.Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.
in the vicinity of : 在 ... 附近
例句：The family's annual income is in the vicinity of $15000.
这家一年的收入在一万五千美元左右。
3.Every solid object will reflect a sound, varying according to the size and nature of the object.
according to ：根据，取决于
例句：Please arrange the books according to size.
请按大小将书分类。
4.So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
a shoal of ：大量，大群
例句：Emigration had carried to its shores shoals of men and women.
移民使成群结队的男男女女来到了它的海岸。
5.It has been found that certain bats emit squeaks and by receiving the echoes, they can locate and steer clear of obstacles -- or locate flying insects on which they feed.
steer clear of ：避开
例句：Kids should steer clear of that park, it doesn't seem safe.
那个公园好像不安全,孩子们应该避开。
feed on ：以 ... 为食物
例句：Cows feed on hay.
牛以干草为食。
6.This echo-location in bats is often compared with radar, the principle of which is similar.
compare with ：与 ... 比较
例句：The output of the factory this year has increased by 20 percent as compared with last year.
这家厂今年的产量比去年增加了百分之二十。
注意比较：compare to 把...比作
He compared the girl to the moon in the poem.
他在诗中把那姑娘比作月亮。
Key Structures
So was born the echo-sounding apparatus, now in general use in ships.
本句是一个倒装句，正常语序是：The echo-sounding apparatus was so born, now in general use in ships.
这里用倒装，目的有三：一是出于修辞的需要，使句子不至于显得头重脚轻；二是对方式状语so进行强调；三是起到使本句同上文连接更为紧凑的作用。
