Death is inevitable and the thoughts of it alone sends cold through my veins.
The options are very difficult and I can't imagine myself doing any of them easily. A shark won't spare a human after biting and the taste of blood will attract other wild fishes.
Elephant is a no go area and jumping from the airplane should do. I have a phobia for height and I might probably die out of fear.
Have you thought of landing into water after jumping from that height? Still a feast for sharks.. Lol
The thing with jumping from that height is that you can't breath due to low oxygen which will lead to one's death even before getting into the water. Also, if one jump from that height, the person will end inside the bottom of the water because of the speed that comes with the fall. It is still the easiest among the other two.