Final answer:
The concordance rate for bipolar disorder among identical twins is high; common.
Step-by-step explanation:
The correct answer is d) high; common.
Bipolar disorder has a high concordance rate among identical twins, which suggests a strong genetic influence. If the concordance rate was low, it would indicate that genetic factors play a smaller role in the development of the disorder.
An example of a high concordance rate for bipolar disorder among identical twins is the Minnesota Twin Family Study, which found that the concordance rate for bipolar disorder was around 67% for identical twins.