Two identical straight wires are stretched so as to produce 6 beats per second when vibrating simultaneously. On changing the tension in one of them, the beat frequency remains unchanged. Denoting by \[{{T}_{1}},\,{{T}_{2}}\], the higher and the lower initial tensions in the strings, then it could be said that while making the above change in tension [IIT 1991]

• A.            \[{{T}_{2}}\] was decreased  
• B.            \[{{T}_{2}}\] was increased
• C.            \[{{T}_{1}}\] was increased   
• D.            \[{{T}_{1}}\] was kept constant