The correct answer is A) Cut the sea painter and clear the vessel. After launching an inflatable liferaft, one of the first actions should be to cut the sea painter (the line that tethers the liferaft to the vessel) and clear the liferaft from the sinking or drifting vessel. This is a critical safety step to prevent the liferaft from being pulled down or damaged by the sinking vessel. The other options, while important, are not as time-sensitive as this initial action to disconnect the liferaft from the vessel. Inflating the liferaft floor (B), deciding on rations (C), and opening the equipment pack (D) are all necessary steps, but they should be addressed after the liferaft has been safely cleared from the vessel.