单项选择题 An aircraft has indicated that he wants you to change course and follow him. You cannot comply because of an emergency on board. Which signal should you make?（）

单项选择题 All self-propelled vessels on an international voyage must be equipped with how many Emergency Position Indicating Radio beacons (EPIRB)? （）

单项选择题 After having activated the emergency position indicating radio beacon，you should（）.