In a hospital$-$based case$-$control study aiming to study the relationship between bronchitis and lung cancer, the researchers selected patients with bronchitis from the same hospital to serve as the control.

This selection of the control group is problematic because it

$$a$.$ Can result in differential selection of cases

$$b$.$ Results in attrition bias

c$.$ Can increase type I error

d$.$ Can inflate the type Il error