The two nearest harmonics of a tube closed at one end and open at other end are $220\text{Hz}$ and $260\text{Hz}$. What is the fundamental frequency of the system?

1. A
   $10\text{Hz}$
2. B
   $20\text{Hz}$
3. C
   $30\text{Hz}$
4. D
   $40\text{Hz}$