Final answer:
Leonardo da Vinci unified the composition of the Last Supper by grouping the apostles into four groups of three figures, which references the Holy Trinity and brings a sense of geometric harmony to the painting.
Step-by-step explanation:
The Unified Composition in Leonardo's Last Supper
Leonardo da Vinci unified the composition of the Last Supper by organizing the apostles into four groups of three figures. This structure serves several symbolic purposes. First, it creates a geometric harmony within the painting, suggesting the notion of a pyramid, which creates an illusion of space and a sense of three-dimensionality. Second, it encapsulates elements of Neo-Platonism, reflecting the idea of geometric shapes representing heavenly perfection, and celebrates Christ as the embodiment of heaven on earth.
The division into groups of three also references the Holy Trinity, a central concept in Catholic theology. This is further reinforced by the three windows in the background of the painting, which some interpret as an allusion to the Trinity. Moreover, the gestures and gazes of the figures toward one another within these groups create a visual dialogue that unifies the composition, setting Leonardo's work apart from earlier Renaissance iterations where figures often appeared more isolated.
In summary, the correct answer to the question is C. Four groups of three figures.