According to One Theory, People Develop a Phobia of an Object

According to one theory, people develop a phobia of an object if they see that object and then feel pain. Evidence against this simple theory includes the fact that

A) many people have phobias of objects with which they have had no unpleasant experiences.
B) systematic desensitization is an effective way of treating phobias.
C) anyone who is successfully treated for one phobia immediately develops another one.
D) the most common objects of phobias are totally harmless objects such as trees and houses.