One Problem with Attempting to Study the Effects of Nonshared

One problem with attempting to study the effects of nonshared family environment is that

A) there are myriad environmental variables that affect personality, but each may have only a small effect.
B) the nonshared environmental effects on each child in the family are too subtle to analyze with current methods.
C) the effects of shared family environments interfere with clearly observing the effects of the nonshared family environments.
D) the equal environments assumption is violated by variables attributable to nonshared family environment.