Recent Studies of the Connection Between Specific Genes and Aspects

Recent studies of the connection between specific genes and aspects of temperament have demonstrated that

A) most temperamental capacities have no genetic component.
B) genetic temperamental tendencies are sometimes more likely to be expressed when the family environment is suboptimal and sometimes when it is optimal.
C) individual differences in positive emotions tend to be more genetically based than are individual differences in negative emotions.
D) Recent studies have demonstrated all of these.