Why Are Adoption Studies Often Used When Attempting to Study

Why are adoption studies often used when attempting to study the influence of genetic factors on psychological disorders?

A) because they allow examination of genetic influences of psychopathology using more sophisticated statistical techniques
B) because they allow examination of genetic influences of psychopathology without the typical confound of having siblings raised in the same environment
C) because they allow examination of genetic influences of psychopathology without the typical confound of common biological parents
D) because they allow examination of genetic influences of psychopathology through direct examination of genetic causes