托福听力背景知识：Sunflower

　　common name for annual and perennial herbs of a genus of the family of composite flowers. The genus, which contains about 67 species, is thought to be native to South America originally, although sunflowers are now distributed almost worldwide. Some of the tall-growing forms may attain a height of 3 m (12 ft). The large, solitary blossom, sometimes as large as a meter in diameter, is composed of yellow ray flowers and a central disk of either yellow, brown, or purple flowers, depending on the species. The daily orientation of the flower to the sun is a direct result of differential growth of the stem. A plant-growth regulator, or auxin, accumulates on the shaded side of a plant when conditions of unequal light prevail. Because of this accumulation, the darker side grows faster than the sunlit side. Thus, the stem bends toward the sun.

　　waxing方法制作

　　Cire Perdue (French, ¡§lost wax¡§), process of wax casting used in making metal sculpture. A model is coated with wax. The solidified wax is encased in a two-layer mold of plaster or clay. It is then melted or otherwise removed from the mold, and metal is poured into the space where the wax had been. After cooling, the mold is broken to free the metal object. This ancient method is used to produce sculpture, jewelry, and utilitarian products such as dentures.