how is this not A?

Hi Tyler808, I don't think there are any necessary conditions in the argument. Until the last sentence, everything is correlated- we are never told thatX must be the case, or any other sufficient or necessary language. Even when we see the last sentence, we are only told that the disease is A cause of high blood pressure, rather than THE cause. If something is only one among many causes of a phenomenon, that thing is not a necessary condition. The flaw here is that the author confuses the direction of causality, or indeed that one can draw causality from a correlation. This fits much better with C.