The correct answer is C) The suit must, without assistance, turn an unconscious person's mouth clear of the water within 5 seconds. This is a requirement for immersion suits as per the regulations set by the US Coast Guard. The suit must be designed to automatically turn an unconscious person's face out of the water within 5 seconds, without any external assistance, to prevent drowning. The other options are incorrect - the collar does not need to be inflated before abandoning ship, the suit is not designed to withstand prolonged exposure to flame and burning, and the suit is not meant to provide weeks-long protection against hypothermia, but rather short-term protection against cold water immersion.