A is incorrect, many people who have diagnosed Anxiety have developed new phobias because of fear but not everybody diagnosed has developed new fears/phobias.
B is correct in many cases adults with anxiety tend to want to stay to themselves but find relief in knowing they have access to communication with friends.
C is definitely incorrect, simply for the patient being an adult and somehow never having anxiety or stress about a new situation.
D is incorrect. cases of anxiety in adults have been treated with medication but not every patient has needed to take medication to relieve their phobias, fear, stress, etc.