A certain unit organizes employees to conduct medical examinations, and employees can voluntarily sign up to participate. Pharaoh met Xiao Li, a newcomer, and talked about this. Pharaoh reminded Xiao Li: "Where is the organization organizing a physical examination, hurry up and register. " Xiao Li said, "I'm in good health, so I don't need to report. ". Which of the following can be used as a hypothesis in Xiao Li's answer? ? ['If you are not healthy, you must sign up for a medical examination.', "As long as I am healthy, I don't have to take a physical examination.", 'Whoever signs up for the medical examination is unhealthy.', 'Only people who are not healthy can sign up for the medical examination.']