For the average person who needs a transfusion, blood from a relative is more likely to be infected with hepatitis than is blood from a blood bank. Ttherefore, the risk of contracting hepatitis from a transfusion is higher for people receiving blood from relatives than for people receiving blood from blood banks. Which one of the following, if true, most seriously weakens the argument? ['Blood transfusions only rarely result in the recipient being infected with hepatitis.', 'Donors to blood banks are always asked whether they have ever been infected with hepatitis.', "Blood taken from a relative is highly likely to match a transfusion recipient's blood type.", 'Blood that is to be used in a transfusion is always screened for hepatitis.']