How much of American GNP comes from sectors that are affected by climate change

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.

A．Pebbles tossed into the air make no sound that can be heard by human ears.
B．A bat will catch hundreds of moths in a single hour.
C．Insect-eating bats are totally blind.
D．The sonar system of bats is as good as man-made sonar.