Which of the following must be true if firms are exiting a perfectly competitive industry in the long run? Firms are earning negative economic profit, causing firms to exit, the price to rise, and profits will become positive in the long run. Firms are earning positive economic profit, causing firms to exit, the price to rise, and profits will become zero in the long run. Firms are earning zero economic profit, causing firms to exit, the price to rise, and profits will eventually become positive in the long run. Firms are earning negative economic profit, causing firms to exit, the price to rise, and profits will eventually reach zero in the long run.