Option-B
SImple reason for this.Use your intuition like below way
Find all the shortest path from each node to other and mark your visited edge .Then automatically in first searching u will find that only two edge are unused example edge R1---->R2 as well as R4---->R6.
When u change it into 2,Then again apply your intuition to find out shortest path from each node to other in this satuation u again find on link is unused.