Best Answer - Chosen by the Asker
1. You show up an hour late. An American would ask, "What HAPPENED to you?" (A one-time occurrence.)
2. Your personality has altered for the worse over the past few weeks. An American would ask, "What HAS HAPPENED to you?" (A process that occurred over time.)
3. An American asks, "Have you lost all your money?" "No, that's not it," you reply. "Well, then, what DID HAPPEN to you?" (A contrast from a previous theory.)
