The below image clearly explains it can be any of those IDs
As you can see we dont have same network ID for all 3.
Had the option d been only 224 and 240 in the third octet then , both A and B are correct. But
As we have different nid for all, the SM can be different for all and based on how many subnets you want to create
With 224 you can create 6 different sub networks
With 240 you can create 14 different subnetworks
With 248 you can create 30 different subnetworks.