2019届高考英语人教版选修七要点点拨课件:unit 3
2019届高考英语人教版选修七要点点拨课件:unit 3第5页

Like some animals, dolphins use sound to help them find their way around. They also make these sounds to talk to each other and to help them find food. We now know they do not use their ears to receive these sounds, but the lower part of the mouth,called the jaw.