Water waves with wavelength $\lambda$ are travelling normally towards an obstacle that has a narrow opening. The opening has a width equal to $\lambda$. The waves leaving the opening spread out through an angle $\theta$, as illustrated. The opening is then gradually made wider. What, if anything, happens to $\theta$ and to the wavelength of the waves after they pass through?
- A$\theta$ decreases, wavelength remains the same
- B$\theta$ increases, wavelength remains the same
- C$\theta$ remains the same, wavelength decreases
- D$\theta$ remains the same, wavelength increases