A、Because they have no sisters or brothers. B、Because they are overprotected by their parents. C、Because their parents expect to

The key question for any only child is this: why were you an only child? It’s a key question for at least two reasons. If your parents had wanted several children but could have only you, they are most likely to pour into you all the energy and attention that had been intended for several children. I call this the "special jewel" phenomenon. Only children who are special jewels often arrive when their parents are older--usually in their thirties. These special jewels can become very spoiled and self-centered.
    On the other hand, you may be an only child because your parents planned for only one and stuck to their plan. Your parents may give you a very strict and very well-structured education to make you "a little adult". Many only children grow up feeling unhappy because they always had to be such "little adults".