The diagrams illustrate a wave on the water surface in a tank at times $1.0\ \text{s}$ apart. The wave is generated at P and moves to the right. Which row gives the frequency and the speed of this water wave?
- A$2.0\ \text{Hz},\ 4.0\ \text{cm s}^{-1}$
- B$2.0\ \text{Hz},\ 8.0\ \text{cm s}^{-1}$
- C$4.0\ \text{Hz},\ 4.0\ \text{cm s}^{-1}$
- D$4.0\ \text{Hz},\ 8.0\ \text{cm s}^{-1}$