Which of the Following Describes One of the Most Important

Which of the following describes one of the most important features of the Katsura Imperial Villa, and why?

A) All the windows open to the outside in order to achieve the harmonious integration of building and garden.
B) The doors can open to the outside in order to achieve the harmonious integration of building and garden.
C) All the rooms are small and rectangular in order to achieve a harmonious integration.
D) The inner courtyard provides access to the garden views in order to achieve harmonious integration of building and garden.