One of the Things That an Alien Observing the Industrialized

One of the things that an alien observing the industrialized world might find very puzzling about people's behaviour is

A) people behave rationally in order to ensure that they have long,healthy lives.
B) people manage to notice only their important physical symptoms and disregard the rest.
C) at least half of all deaths are linked with behaviour that is under people's own voluntary control.
D) almost all of deaths are linked with behaviour that is under people's own voluntary control.