How is the external flotation bladder of an immersion suit inflated?

A
It is inflated by a small CO2 bottle that is automatically tripped when the front zipper is at the top of the zipper track.
B
It is inflated by a small CO2 bottle that is manually tripped.
C
It is inflated by blowing through an inflation tube.
D
It inflates by sea water bleeding into the flotation bladder and reacting with a chemical therein.
E