In air, the speed of sound is $330\ \text{m s}^{-1}$. In air, ultraviolet waves travel at $3.0\times10^8\ \text{m s}^{-1}$. Which row shows a possible frequency and speed for an ultrasound wave in air?
- Afrequency $4000\ \text{Hz}$, speed $330\ \text{m s}^{-1}$
- Bfrequency $4000\ \text{Hz}$, speed $3.0\times10^8\ \text{m s}^{-1}$
- Cfrequency $40000\ \text{Hz}$, speed $330\ \text{m s}^{-1}$
- Dfrequency $40000\ \text{Hz}$, speed $3.0\times10^8\ \text{m s}^{-1}$