question: Q:Drug A is an experimental compound being investigated for potential use as a protectant against venous thrombosis. Binding assays reveal that the drug’s primary mechanism of action is to block carboxylation of glutamic acid residues in certain serum proteins. Drug A is most similar to which of the following:? 
  {'A': 'Steptokinase', 'B': 'Heparin', 'C': 'Rivaroxaban', 'D': 'Bivalirudin', 'E': 'Warfarin'},