Cats spend much of their time sleeping; they seem to awaken only to stretch and yawn. Yet they have a strong, agile musculature that most animals would have to exercise strenuously to acquire. Which one of the following, if true, most helps to resolve the apparent paradox described above? ['Many other animals also spend much of their time sleeping yet have a strong, agile musculature.', 'Cats derive ample exercise from frequent stretching.', 'Cats require strength and agility in order to be effective predators.', 'Cats have a greater physiological need for sleep than other animals.']