TOEFL Reading: ETS-TOEFL阅读机经 - S31MBB2JTS84RN_7L$

The author mentions a "stereo speaker" in the passage in order to A. contrast the ways in which humans and insects magnify their sounds B. compare the ranges of sounds produced by humans and insects C. support the claim that small size is a disadvantage for insects that produce calls D. help explain how small insects magnify the sounds of their calls