Chronic diseases are more common today than in the past in developed countries due to a decreased malnutrition b increased access to clean water c population decline d better health care e longer life expectancies

The correct answer is - e. longer life expectancy.

The chronic diseases most commonly affect the older population, due to the weakening of the body as it gets into the latter stages of its existence. Since the life expectancy has increased significantly in the last century, and it is further increasing, even though with lower tempo nowadays, there's more and more people that reach older life, thus the number and percentage of the chronic diseases is ever-growing, especially in the developed countries where the population is in general aging as well.