Final answer:
The innovative feature of Andrea Palladio's villas is the Palladian window, a characteristic architectural element distinct from the Gothic flying buttresses and not to be confused with geodesic domes or general rotunda concepts.Option D is the correct answer.
Step-by-step explanation:
Among the innovative features of the villas designed by the renowned Renaissance architect Andrea Palladio, one can identify the Palladian window as a key element. Flying buttresses were primarily a feature of Gothic architecture, designed to support taller, thinner walls and allow for more stained glass windows, as seen in cathedrals of that period. Geodesic domes, although an architectural innovation, were not a feature of Palladio's work but are more associated with the 20th-century architect Buckminster Fuller.
The concept of the rotunda, exemplified by the Pantheon's dome in ancient Rome, certainly influenced Palladian architecture, but the specific term 'Rotunda' refers to any round building or room, especially one covered with a dome. Palladio is especially known for his use of the Palladian window, a large central arched window flanked by two smaller, square-topped windows, which became an iconic and integral element of his villa designs and of Palladian architecture in general.