The music chip that is connecting the phone to the power supply in the mobile phone shop is suspended in the jar, and the air is gradually extracted.
D hang a talking mobile phone, an electric bell or a music chip connected to the power supply in a jar, and then pump the air out of the jar, as shown in the figure. The sound gradually becomes smaller, but the sound can always be heard. The reason is that there is still a small amount of air in the bottle, and the solid hanging from the sound source can also transmit sound. Choose D.