Final Answer:
The small, concave curve joining the shaft of a classical column to its base, also known as apophysis, is referred to as an Apophyge. The correct option is A.
Step-by-step explanation:
In classical architecture, the apophyge is a distinctive feature found in the transition between the shaft and the base of a column. It is a small, concave curve that serves as a visual and architectural transition element. The apophyge is located just above the actual base of the column and creates a subtle curvature in the overall design.
Options B, C, and D represent other architectural elements but do not specifically refer to the small, concave curve known as apophyge. The correct identification of architectural features is crucial in understanding and appreciating classical column design.
Option A is the answer.