Answer
The system could be:
(b) a tube of air open at one end
Work Step by Step
A pipe that is closed at one end can only produce odd harmonics. That is, the pipe can produce $f_1, ~3f_1, ~5f_1, ~7f_1,~9f_1,~etc...$
If $f_1 = 50~Hz$, then the three lowest frequencies are $50~Hz, 150~Hz,$ and $250~Hz$.
The system could be:
(b) a tube of air open at one end
