Final answer:
A nurse using Nightingale's theory focuses on the patient and the environment to promote healing, highlighting the significance of a supportive environment in the patient's recovery process.
Step-by-step explanation:
The behavior that indicates a nurse is using Nightingale's theory to plan nursing care is when the nurse thinks about the patients and patients' environments.
Florence Nightingale's theory emphasized the importance of the environment in healing and she believed that nurses should create the best conditions for the body to repair itself.
Hence, a nurse guided by her theory would pay special attention to factors such as cleanliness, ventilation, warmth, light, and quietness, as well as proper nutrition and hygiene for the patient.