The diagram depicts two tubes. Apart from the ends, tube X and tube Y are the same; the lower end of tube X is closed, whereas the lower end of tube Y is open. The upper end of each tube is open. A tuning fork held above tube X makes the air resonate at frequency $f$. With tube X, there is no resonance at any frequency below $f$. Which tuning fork will cause resonance when positioned just above tube Y?
- Aa fork of frequency $\frac{f}{2}$
- Ba fork of frequency $\frac{2f}{3}$
- Ca fork of frequency $\frac{3f}{2}$
- Da fork of frequency $2f$