Why Would a Researcher Use an Elimination Criterion Like "Must

Why would a researcher use an elimination criterion like "Must not have baseline liver function tests that are outside the normal range"?

A) Impaired liver function may have been identified by the researcher as an extraneous variable.
B) The intervention planned by the researcher could have an adverse effect on individuals with impaired liver function.
C) Liver function tests are possibly being measured in order to detect the independent variable's effect on the dependent variable.
D) The researcher is attempting to eliminate persons with all laboratory tests that are outside normal range.
E) The dependent variable may be abnormally elevated in persons who do not have normal liver function.