[填空题]

Our theories about human disease are the product of current fashion 1. ______.
than we would like to admit. But just as the moment influences the hemline
and the automobile fender, so too a type of intellectual currency 2. ______.
affect our understanding of how illness happens. Much of
the 20th century is spent in pursuit of external causes of 3. ______.
disease - cigarettes, fatty foods, tick bites. Rather like the hero in an old western,
medicine’s work was to track down the bad guys, round them up 4. ______.
and squish them before a real commotion. Antibiotics, vaccines,
heart pi