Refer to the exhibit. HSRP has been configured and Link A is the primary route to router R4.  When Link A fails， router R2 （Link B） becomes the active router. 
Which router will assume the  active role when Link A becomes operational again？" （）

A. The primary router R1 will reassume the active role when it comes back online.
B. The standby router R2 will remain active and will forward the active role to router R1 only in the  event of its own failure.
C. The standby router R2 will remain active and will forward the active role to router R1 only in the  event of Link B failure.
D. The third member of the HSRP group， router R3， will take over the active role only in event of  router R2 failure.