Below are steps that can occur in an enzyme reaction. A. E (or E') binds A B. E (or E') binds B P. P is produced Q. Q is produced In a double displacement reaction, A + B -> P + Q the order of events is: (put A, B, P, or Q in each spot. If multiple steps can potentially occur at that stage, put AB, BP, ABQ, etc. for each step that could happen at a particular step). It is therefore possible that some answers may be appropriate in more than one step. First step . Second step . Third step . Fourth step .