Leatherbacks, the largest of the sea turtles, when subjected to the conditions of captivity, are susceptible to a wide variety of fatal diseases with which they would never come in contact if they lived in the wild. It is surprising, ttherefore, that the likelihood that a leatherback will reach its theoretical maximum life expectancy is about the same whether that animal is living in captivity or in the wild. Which one of the following, if true, most helps to resolve the apparent discrepancy? ['The size of a leatherback is an untrustworthy indicator of its age.', 'Most leatherbacks that perish in the wild are killed by predators.', 'Fewer diseases attach leatherbacks than attack other large aquatic reptiles.', 'The average life expectancy of sea turtles in general is longer than that of almost all other marine animals.']