A．By adding sound proofing. B．By planting vegetation. C．By wearing ear protection. D．By separating residential areas.
单项选择题Which sound can most people's ears pick up（）
A．Sounds of 15,000 hertz. B．Sounds of 20,200 hertz. C．Sounds of 30,000 hertz. D．Sounds of 50,000 hertz.
单项选择题What is most noise pollution damage concerned with（）
A．Objects. B．Intensity. C．Rate. D．Frequency.
