According to Barlow (2002)and Others,all the Evidence Now Points to What

According to Barlow (2002) and others,all the evidence now points to what conclusion about agoraphobic avoidance behaviour?

A) It is conceptually unrelated to panic disorder; it is a coincidence that they often occur together.
B) It is similar to the behaviour of people with generalized anxiety disorder.
C) It is a complication of severe unexpected panic attacks.
D) It is a principle cause of panic disorder.