Suppose P, Q, R, S, C are five natural language statements that form an argument with premises P, Q, R, S and conclusion C. Suppose also that the argument is valid. Which of the following would not on its own be an explanation for why the argument is valid? Necessarily, if P and R are true, so is C. C couldn't be false. OR couldn't be true. OP, Q, and S are jointly impossible. OP, Q, R, and C are jointly impossible