In these days of technological triumphs，it is well to remind ourselves from time to ti

me that living mechanisms are often incomparably more efficient than their artificial imitations.There is no better illustration of this idea than the sonar (声纳) system of bats.Ounce for ounce，and watt for watt，it is billions of times more efficient and more sensitive than the radars and sonars contrived (发明) by man.Of course，the bats have had some 50 million years of evolution to refine their sonar.Their physiological mechanisms for echo location，based on all this accumulated experience，therefore merit our thorough study and analysis.To appreciate the precision of the bats‘ echo location，we must first consider the degree of their reliance upon it.Thanks to sonar，an insect-eating bat can get along perfectly well without eyesight.This was brilliantly demonstrated by an experiment performed in the late eighteenth

century by the Italian naturalist Lazzaro Spallanzani.He caught some bats in a bell tower，blinded them，and released them outdoors.Four of these blind bats were recaptured after they had found their way back to the bell tower，and on examining heir stomachs‘ contents，Spallanzani found that

they had been able to capture and gorge themselves with flying insects.We know from experiments that bats easily find insects in the dark of night ， even when the insects emit no sound that can be heard by human ears.A bat will catch hundreds of soft-bodied，silent-flying moths or gnats in a single hour.It will even detect and chase pebbles or cotton spitballs tossed into the air.

16.According to the author，the sonar system of bats is an example of the idea that.()

A.this is the age of technological triumphs

B.modern machines are inefficient

C.living mechanisms are often more efficient than man-made

machines

D.artificial imitations are always less efficient than living

mechanisms

17.The author suggests that the sonar system of bats ().

A.was at the height of its perfection 50 million years ago

B.is better than man-made sonar because it has had 50 million years to be refined

C.would have been discovered by man many years ago

D.is the same as it was 50 million years ago

18.The fact that“blind bats”will detect and chase cotton spitballs as well as insects is remarkable because.()

A.bats do not eat spitballs

B.cotton is harder to track

C.Spitballs make no sounds audible to human ears

D.there is purpose in the flight of insects

19.This passage was written to illustrate().

A.the deficiencies of man-made sonar

B.the dependence of man upon animals

C.that we are living in a machine age

D.that the sonar system of bats is remarkable

20.Which of the following is the main point of the passage？()

A.A bat will catch hundreds of gnats in a single hour

B.Here is a perfection in nature which sometimes cannot be matched by man‘s creative efforts

C.The phrase“blind as bat”is valid

D.director of NIH learned of the abuse