Astudy was done on the mortality (live vs. die) of two major hospitals: carebetter and treatmore. data were collected over a period of time from five major illnesses and it was found that carebetter does better overall (i. e., has a smaller percentage of deaths). however, in each of the five illnesses separately, treatmore does better. which of the following is correct?

a. this is an example of simpson's paradox.
b. "illness" is a lurking variable in this example.
c. both (a) and (b) are correct
d. this is an example of a negative association between variables
e. this situation is mathematically impossible.