Final answer:
The Parthenon, a temple located on the Acropolis in Athens, Greece, was constructed with various optical refinements, including curving the columns slightly, to create the illusion of symmetry and perfection.
Step-by-step explanation:
The correct answer is a) Columns, top, symmetrical.
The Parthenon, a temple located on the Acropolis in Athens, Greece, was constructed with various optical refinements in order to create the illusion of symmetry and perfection to the viewer. One of these refinements is the slight upward curve given to the base of the columns, which compensates for the way the human eye perceives straight lines. By curving the columns slightly, the architects Iktinos and Kallikrates made the Parthenon appear perfectly symmetrical.