`0.001` mol of `Co(NH_(3))_(5)(NO_(3))(SO_(4))` was passed through a cation exchanger and the acid coming out of it required 20 ml of 0.1 M NaOH for neutralisation. Hence, the complex is
A. `[CoSO_(4)(NH_(3))_(5)]NO_(3)`
B. `[CoNO_(3)(NH_(3))_(5)]SO_(4)`
C. `[Co(NH_(3))_(5)]SO_(4)NO_(3)`
D. none of these