A. Only the account that has purchased the RI will get the advantage of RI pricing
B. One instance of a small size and running in the US-East-1a zone of each AWS account will get the benefit of RI pricing
C. Any single instance from all the three accounts can get the benefit of AWS RI pricing if they are running in the same zone and are of the same size
D. If there are more than one instances of a small size running across multiple accounts in the same zone no one will get the benefit of RI