Choose the correct statement about the U. S. short-run Phillips curve. A. The U. S. short-run Phillips curve has been shifting steadily downward since 2001. B. U. S. inflation and unemployment data cannot be interpreted in terms of the short-run Phillips curve. C. We can interpret U. S. inflation and unemployment data in terms of a shifting short-run Phillips curve, which sometimes shifts upward and sometimes shifts downward. D. The U. S. short-run Phillips curve has been shifting steadily upward since 2001.