In Nightingale's mind,the specific "scientific" activity of nursing that was the central element in health care,without which medicine and surgery would be ineffective,is which of the following:

A) Preparing nutritious meals.
B) Maintaining an aesthetic environment.
C) Maintaining hygiene.
D) Sustaining a quiet environment.

Nightingale believed that maintaining proper hygiene was the key scientific activity of nursing, as it could prevent the spread of disease and infection. She emphasized the importance of cleanliness in hospitals, including regular hand-washing, sanitation of equipment and bedding, and proper disposal of waste. Without these measures, medicine and surgery would be ineffective in preventing the spread of disease. While preparing nutritious meals, maintaining an aesthetic environment, and sustaining a quiet environment are also important aspects of patient care, they are not the central element that Nightingale identified as critical to effective health care.