In these days of technological triumphs, it is well to remind ourselves from time to time that living mechanisms are often incomparably more efficient than their artificial imitations. There is no better illustration of this idea than the sonar 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 designed 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 Lazure 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 their stomachs' contents, Spallanzani found that they had been able to capture and fill 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 in a single hour. It will even detect and chase pebbles tossed into the air.
　　
6. The passage is mainly about _____.
[A] living mechanisms and their artificial imitations
[B] the remarkable sonar system of bats
[C] the deficiencies of man-made sonars
[D] the experiment of "blind-bats"

7. Where of the following statements is true?
[A] Living mechanisms are always more efficient than their artificial imitations.
[B] Bats rely on their sonar system as well as eyesight to eat insects.
[C] The sonar system of bats has had 50 million years to be refined.
[D] People have discovered the bats' sonar system thousands of years age.

8. Lazzoro Spallanzani demonstrated that a bat can get along well without eyesight through _____.
[A] He caught soem bats and blinded them and released them.
[B] Four of these blind bats found their way back.
[C] He recaptured the four returned bats.
[D] The stomachs' of the blind bats found to be fill with flying insects.

9. Bats find insects in the dark of night with the help of _____.
[A] echoes
[B] eyesight
[C] sound waves
[D] none ofthe above

10. Implied but not stated _____.
[A] Pebbles tossed into the air make no sound that can be heard by human ears
[B] A bat will catch hundreds of months in a single hour
[C] Insect-eating bats are totally blind
[D] The sonar system of bats is as good as man-made sonar