arketed last year by a Welsh pany. It is an ear-splitting 17-kilohertz buzzer (蜂鸣器) designed to help shopkeepers get rid of young people hanging around in front of their stores. Humans can hear sounds taking place in a frequency range between 200 and 20,000 hertz,as the research shows. But our hearing gradually es worse when we grow up.Р68.Students in some Manhattan schools have begun using the technology,so they can_________.Р A.talk in class without being heard by their teachersРB.use cellphones to send messages in classР C.hear better in class than their teachersРD.improve their hearing abilityР69.The underlined phrase “the other way around” implies the ________.РA.adults are annoyed nowРB.teenagers are annoyed nowРC.adults are not annoyed nowРD.both adults and teenagers are annoyed now
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