The amplitude of vibration of a particle is given by \[{{a}_{m}}=({{a}_{0}})/(a{{\omega }^{2}}-b\omega +c);\] where \[{{a}_{0}},a,b\] and c are positive. The condition for a single resonant frequency is [CPMT 1982]

• A.            \[{{b}^{2}}=4ac\]                
• B.            \[{{b}^{2}}>4ac\]
• C.            \[{{b}^{2}}=5ac\]                
• D.            \[{{b}^{2}}=7ac\]