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

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

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 ago.