Which material is mainly used in terracotta art?

Correct answer: Baked clay

Terracotta is a form of clay craft. Artists begin with natural clay, remove unwanted stones or particles, and shape the moist material into pots, figures, tiles, ornaments, or other objects. The shaped piece is then dried and heated in a kiln or another suitable high-temperature setting. Firing makes the clay hard and gives the finished object its characteristic earthen appearance, although it may later be decorated or glazed.

Therefore, baked clay is the main material used in terracotta art, so option A is correct. The name itself is associated with fired or baked earth, which provides a useful memory link. The other choices are not materials used as the primary substance for ordinary terracotta work: glass water, paper currency, and rubber oil are unrelated. The essential process is shaping clay and baking it until it becomes firm.