What Distress signals, whether used together or separately, mean that grave and imminent danger threatens and immediate assistance is requested

A signal made by radiotelegraphy or by any other signaling method consisting of the group SOS (…___... in the Morse Code). ii. A signal sent by radiotelephony consisting of the spoken word MAYDAY; iii. Rockets or shells throwing red lights, fired one at a time at short intervals; and iv. A parachute flare showing a red light;