单项选择题

This 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"

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单项选择题

Bats find insects in the dark of night with the help of ______.

A．echoes
B．eyesight
C．sound waves
D．none of the above

单项选择题

What does the author imply when he mentions living cells in Paragraph 3

A．The research has involved living creatures.
B．The results from the lab test might not always be reliable.
C．If it is tested in living body, the results will be the same.
D．The chemistry of VC is livin