资料题：In Line2, the word ''step" could best be replaced by（　）。

George Washington Carver showed that plant life was more than just food for animals and humans.Carver's first step was to analyze plant parts to find out what they were made of.He then combined these simpler isolated substances with other substances to create new products.The branch of chemistry that studies and finds ways to use raw materials from farm products to make industrial products is called chemurgy(农业化工).Carver was one of the first and greatest chemurgists of all time.Today the science of chemurgy is better known as the science of synthetics.Each day people depend om and use synthetic materials made from raw materials.All his life Carver batted against the disposal of waste materials, and waned of the growing need to develop substitutes for the natural substances being used up by humans.Carver never cared about getting credit for the new products he created.He never tried to patent his discoveries or get wealthy from them.He turned down many offers to leave Tuskegee Institute to become a rich scientist in private industry.Thomas Edison, inventor of the electric light, offered him a laboratory in Detroit to carry out food research when he was in the United States Department of Agriculture.At the peak of his career, Carver's fame and influence were known on every continent.