Final answer:
The recommended position for postural drainage of the left upper lobe - posterior lung segment in an adult is Left Side-Lying.
Step-by-step explanation:
The recommended position for postural drainage of the left upper lobe - posterior lung segment in an adult is Left Side-Lying. This position allows gravity to assist in the drainage of secretions from the lungs by positioning the affected area to be in a dependent position. By lying on the left side, the left upper lobe - posterior lung segment will be in a lower position, aiding in the drainage process.