In 1856, John Stuart Mill Presented Three Methods of Hypothesis

In 1856, John Stuart Mill presented three methods of hypothesis formulation in disease etiology: method of difference, method of agreement, and method of concomitant variation. Which of the following best defines method of agreement?

A) The frequency is common to a number of circumstances where the disease occurs at a high frequency.
B) If the frequency of a disease differs between two locations, it may be because a particular factor varies between those two places.
C) A single factor is common to a number of circumstances where the disease occurs at a high frequency.