As advances in medical research and technology have improved the ability of the medical profession to diagnose and treat a wide variety of illnesses and injuries, life spans have increased and overall health has improved. Yet, over the past few decades there has been a steady and significant increase in the rate of serious infections. Which one of the following, if true, most helps to resolve the apparent discrepancy in the information above? ["Modern treatments for many otherwise fatal illnesses increase the patient's susceptibility to infection.", 'It remains true that doctors sometimes prescribe ineffective medications due to misdiagnosis.', 'Life spans have increased precisely because overall health has improved.', 'As a population increases in size, there is a directly proportional increase in the number of serious infections.']