The correct answer is C) passengers are strapped to their seats. Enclosed lifeboats are designed to be self-righting, meaning they will automatically right themselves after capsizing, but this is only the case if the passengers are properly secured to their seats. The weight and distribution of the passengers plays a critical role in the lifeboat's ability to right itself. If the passengers are not strapped in, they could shift position during a capsize, disrupting the boat's stability and preventing it from righting. The other answer choices, such as deploying a sea anchor or maintaining fuel levels, do not directly impact the self-righting capability of an enclosed lifeboat in the same way as passenger restraints.