Twin Studies Investigating the Heritability of Mental Disorders Reveal That

Twin studies investigating the heritability of mental disorders reveal that _____.

A) mental illnesses are highly heritable; if one twin displays a disorder, the co-twin almost inevitably does
B) identical twins are typically concordant for most mental illness whereas fraternal twins are typically discordant
C) mental illnesses are not heritable attributes
D) for most mental illnesses, the probability of identical twins being discordant for the disorder is greater than their probability of being concordant