According to sigmund freud, an adult who smokes, drinks, overeats, or bites her nails is fixated in the stage of her psychosexual development.

Freud proposed that psychological development in childhood takes place in the following stages (by order): oral, anaI, phallic, latency, and genital.

The oral stage goes from birth to eighteen months of age. The main focus is pleasure seeking through the infant’s mouth, they need to taste and suck. if not,  the infant will be fixated leading to adult habits such as smoking, thumb-sucking, over-eating, and baiting nails.
The answer is oral stage.

Very cool! free points wooo