The correct answer is D) Green star rocket. The green star rocket is the recognized lifesaving signal to indicate the best place to land. This is defined in the International Code of Signals, which is the standard reference for maritime signaling. The green star rocket produces a green flare in the sky, signaling to search and rescue personnel that the location is suitable for landing or approaching a vessel in distress. The other options are incorrect because they represent different types of distress signals with different meanings. Orange smoke signals and red star rockets are used to indicate the location of a vessel in distress, while the horizontal motion of a flag is a general signal to attract attention rather than a specific landing indicator.