when you are redefining a variable, as here you are redefining A as B , both A and B will be pointing to the same address space.. so what ever is the value is there in that addressspace will be present in both the variables A and B. Now if you are moving it in C, address apcae of C wil also have the same value.. means at the end all three variable will have the same value.
redefining in working storage works same as SET ADDRESS OF in procedure division.