Why Are the Rates of Comorbidity (Co-Occurrence) Among Various Anxiety

Why are the rates of comorbidity (co-occurrence) among various anxiety disorders and depression high?

A) because the same psychological interventions should be used on all of them
B) because they share some of the same biological and psychological vulnerabilities for developing them
C) because the diagnostic criteria for these disorders are too ambiguous
D) because they may not be distinct disorders at all