Research on Bipolar Disorder Suggests That One's Likelihood of Having

Research on bipolar disorder suggests that one's likelihood of having the disorder ____.

A) decreases when siblings have the disorder because it is caused by a chance mutation that is unlikely to happen more than once in the same family
B) increases merely by having relatives with the disorder
C) increases only when there is an inherited abnormality and there is exposure to others who have the disorder
D) decreases when there is exposure to others who have the disorder because it can be seen that there is no psychological or social benefit to having the disorder