Final answer:
Freud's three mental structures are the ego, id, and superego. The ego balances the id and superego, the id seeks pleasure, and the superego enforces moral standards.
Step-by-step explanation:
The three mental structures according to Freud's theory of psychoanalysis are the ego, id, and superego. The ego is the reality-based part of our personality that balances the demands of the id and superego. The id is the source of our primitive drives and operates on the pleasure principle, seeking immediate gratification. The superego enforces moral standards and acts as our conscience.