Hard to say from the info provided.
The DR will be selected by highest priority then the highest router ID. Neither the priority non the router IDs are show in this diagram. If we assume that the addresses shown on the router are the router IDs and they all have the same priority R4 should have become the DR in the first place. But the question says that R1 was the DR so some kind of manipulation had to have been going on or it was just the first one to boot.
We can at least assume that C is correct since when R1 reloads there will already be a DR and a BDR it will go into DROTHER. But from there we need guess work. Was R2 the second to boot and there for was the BDR? If so it would be promoted to the DR and the election process would elect R4 as the BDR.
