Why is the same client subnet difficult to load balance across ISGs?

Why is the same client subnet difficult to load balance across ISGs?

A.
Two separate RADIUS accounting sessions must be established as traffic.

B.
Each subnet is associated with a control policy, and the policy server cannot process policy
events from the same policy on different interfaces.

C.
The policy server is unable to identify which ISG the session belongs to.

D.
The ISG requires symmetrical traffic flows, and standard routing cannot determine the return
path for client traffic.