Elizabethans do not understand infection and contagion
as we do. It is not that they are completely ignorant as to
how illnesses spread-physicians believe they know
perfectly well—it is rather that their understanding is
very different from ours. The principal ideas
underpinning most Elizabethan medical thinking come
from Galen, who lived in the second century A.D.
Physicians will cite him as an unquestionable authority
when they explain to you that your health depends on a
balance of the four humors: yellow bile or choler, black
bile, phlegm, and blood.
- The Time Traveler's Guide to Elizabethan England,
Ian Mortimer

What is the central idea of this passage?

O Elizabethan believed that their health depended on
what they ate.
O Elizabethans believed that their health depended
on astronomy
O Elizabethans believed that health depended on the
balance of the four humors.
O Elizabethans believed that health depended on
where one lived.