4. Which of the following best describes the long-run competitive market when there is a rightward shift in demand increase? A. Short-run economic profits are zero, firms enter, long-run economic profits are zero. B. Short-run economic profits are positive, firms exit, long-run economic profits increase. C. Short-run economic profits are positive, firms enter, long-run economic profits are positive. D. Short-run economic profits are positive, firms enter, long-run economic profits are zero