Lesson 7
    5 not __b____ sound made by animals serves as language
    A every b each c the whole d the entire
    6 we have only to turn to that extraordinary discovery of echo-location in bats to see a case ____a__ the voice plays a strictly utilitarian role
    A which b where c when d though
    7 __c____ he shout in the vicinity of a wall, an echo will come back.
    A should b if c when d though
    8 ___d___ the echo-sounding apparatus was born.
    A such b the way c that's how d like thi