To solve this problem, we need to understand why individuals with the 'AB' blood group are called 'Universal recipients'.$\newline \bullet$Blood group 'AB' individuals have both A and B antigens on the surface of their red blood cells (RBCs).$\newline \bullet$The key reason they are universal recipients is due to the absence of antibodies in their plasma.$\newline \bullet$Specifically, they lack both anti-A and anti-B antibodies in their plasma.$\newline \bullet$This absence of antibodies means they can receive blood from any blood group without the risk of an immune reaction.$\newline$Therefore, the correct explanation is:$\newline$Option 4: Absence of antibodies, anti-A and anti-B, in plasma.