First of all, the question stem clearly states that both A and B want to kill C. In other words, the poisoning behavior of A and B is for the purpose of killing C, and both parties have the intention to kill C. C’s subjective intention... Next, we analyze A’s criminal behavior in detail. First determine the causal relationship between the deaths of A and C. Through the three-factor analysis of intervening factors, we can determine that the death of C has nothing to do with A (because you said you can judge by yourself, so I won’t go into the specific judgment process). Since there is no causal relationship between the deaths of A and C, then A's criminal behavior ended when C was seriously injured, and then C drank B's poison and died, which has nothing to do with A... Next, determine the attempted intentional homicide and completed intentional injury. The difference between the two is mainly in subjective and intentional purposes. Intentional homicide is for the purpose of killing, while intentional injury is not for the purpose of killing (the death of the victim is one of the aggravating circumstances, which only affects the severity of the sentencing and does not convert intentional injury into intentional homicide). After understanding this, looking back at the problem, it is obvious that A's poisoning was intentional homicide. Whether the crime of intentional homicide is established or not has nothing to do with whether the victim died. Whether the victim dies or not affects not only the completed or attempted crime of intentional homicide. Here, after C drank A's poison for the first time, he was only seriously injured but not dead. Therefore, A's behavior only constituted attempted intentional homicide.