The current consensus regarding the relationship between attention-deficit/hyperactivity disorder and oppositional-defiant disorder is
d) The two are separate but highly comorbid disorders
What is comorbidity
Comorbidity means that individuals with one disorder are more likely to also have the other.
While they are distinct conditions, there is often an overlap in symptoms, and individuals with ADHD may also exhibit oppositional and defiant behaviors.
However, having one does not necessarily cause the other. Both disorders have their own diagnostic criteria and they can coexist in the same individual