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

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"

A．is supported by VC experts
B．is encouraged by the US government
C．is agreed by medical researchers
D．is disapproved by many scientists