Chronic back pain is usually caused by a herniated or degenerated spinal disk. In most cases the disk will have been damaged years before chronic pain develops, and in fact an estimated one in five people over the age of 30 has a herniated or degenerated disk that shows no chronic symptoms. If chronic pain later develops in such a case, it is generally brought about by a deterioration of the abdominal and spinal muscles caused by insufficient exercise. The statements above, if true, most strongly support which one of the following? ['Four out of five people over the age of 30 can be sure they will never develop chronic back pain.', 'Doctors can accurately predict which people who do not have chronic back pain will develop it in the future.', 'People who exercise their abdominal and spinal muscles regularly are sure to be free from chronic back pain.', 'There is a strategy that can be effective in delaying or preventing the onset of pain from a currently asymptomatic herniated or degenerated spinal disk.']