quEstions 16 to 20 ArE BAsED on thE Following tAlk.

A、thE tEChnology to mAkE mAChinEs quiEtEr hAs BEEn in usE sinCE thE 1930’s.
B、thE tEChnology to mAkE mAChinEs quiEtEr hAs ACCElErAtED inDustriAl proDuCtion.
C、thE tEChnology to mAkE mAChinEs quiEtEr hAs just BEEn in CommErCiAl usE.
D、thE tEChnology to mAkE mAChinEs quiEtEr hAs BEEn invEntED to rEmovE All noisEs.