You could say that “A and B happen to be in sync for a while” is possibility 3, where C is the passage of time. (Unless by “happen to be in sync for a while” you mean that they appear to be correlated because of a fluke.)
You could say that “A and B happen to be in sync for a while” is possibility 3, where C is the passage of time. (Unless by “happen to be in sync for a while” you mean that they appear to be correlated because of a fluke.)