An octahedral complex having molecular composition $Co \cdot 5NH_3 \cdot Cl \cdot SO_4$ has two isomers $A$ and $B$. The solution of $A$ gives a white precipitate with $AgNO_3$ solution and the solution of $B$ gives a white precipitate with $BaCl_2$ solution. The type of isomerism exhibited by the complex is,

• A
  $Co$-ordinate isomerism
• B
  Linkage isomerism
• C
  Ionisation isomerism
• D
  Geometrical isomerism