My best guess would be D. many studies have linked cardiorespiratory exercise to the lowering of blood pressure. (Many studies have also linked going vegan to the lowering of blood pressure, too :)
The process of infection can be broken down into stages, each of which can be blocked by different defense mechanisms. In the first stage, a new host is exposed to infectious particles shed by an infected individual. The number, route, mode of transmission, and stability of an infectious agent outside the host determines its infectivity. Some pathogens, such as anthrax, are spread by spores that are highly resistant to heat and drying, while others, such as the human immunodeficiency virus (HIV), are spread only by the exchange of bodily fluids or tissues because they are unable to survive as infectious agents outside the body.
Droughts
Floods
Their business becomes broke and they lose jobs
Civil war
