A resonant system has a fundamental frequency of 140 Hz. If the next frequencies that are able to give resonance are 280 Hz and 420 Hz the system could be
1
An organ pipe closed at both ends
2
An organ pipe open at both ends
3
An organ pipe closed at one end and open at the other end
4
A taut string vibrating between two fixed points
5
None of the above/More than one of the above.