Why Would a Shared Environment Have Such Little Effect on Personality

Why would a shared environment have such little effect on personality development?

A) A shared environment doesn't mean shared experiences or shared reactions to those experiences; what one sibling perceives as "harsh parenting" could be perceived as "typical" by another.
B) Genetics generally accounts for about 70 percent to 80 percent of the variance explained in personality characteristics; there simply isn't much variation left to be explained by environment.
C) The shared environment cannot be quantified or defined adequately; therefore, any influence it may have on personality development is likely to be haphazard at best.
D) "Shared environment" is not a construct that personality psychologists endorse; rather, it is a concept borrowed from sociology and applied inexpertly to the study of personality.