The correct answer is C. The external flotation bladder of an immersion suit is inflated by blowing through an inflation tube. Immersion suits are designed to provide insulation and flotation in the event of an emergency at sea. The external flotation bladder is inflated manually by the wearer, typically by blowing into an inflation tube located on the suit. This allows the wearer to customize the amount of flotation as needed. The other options are incorrect. The flotation bladder is not automatically inflated by a CO2 bottle (A and B), nor does it inflate by reacting with a chemical when exposed to seawater (D). The manual inflation tube is the standard method for inflating the external flotation bladder on immersion suits.