If a Concordance Rate for a Disorder Is Found to Be

If a concordance rate for a disorder is found to be 60 percent in identical twins,what does this mean? 

A) Genetics play little if any role in either twin's risk for the disorder. 
B) The environment plays little if any role in either twin's risk for the disorder. 
C) The probability of both twins being diagnosed with the disorder is about 60 percent. 
D) If one twin is diagnosed with the disorder, the other twin has about a 60 percent chance of also being diagnosed with the disorder.