Explanation: A transmitter adjusted for a distress call should adhere to internationally recognized frequencies and emission types to maximize the chance of being heard. 500 kHz was historically designated as the international radiotelegraphy distress frequency. This frequency was closely monitored worldwide for distress calls. Regarding emission types: * **Type A-2 (A2A)** refers to modulated continuous wave (MCW) telegraphy. This involves keying an audio tone onto a carrier, producing Morse code signals that are easily recognizable and detectable, even by simpler receivers. * **Type B** emission refers to damped waves, typically generated by spark transmitters. While largely obsolete and generally prohibited for routine communications due to their broad spectrum, damped waves were historically a primary distress emission type because of their distinct sound and ease of detection across a wide range of receivers, especially early ones. Options A and B are incorrect because 600 kHz and 400 kHz were not the designated international radiotelegraphy distress frequencies. "Type C" emission is also not the standard or correct designation for these distress communication types in this context.