A、They produce the same yield in different locations. B、They are suitable to grow only in the United States. C、They produce bett

Thomas Tommy Carter is a plant scientist in North Carolina. He works for the Agricultural Research Service in the United States Department of Agriculture. He leads Team Drought, a group of researchers at five universities. They have been using conventional breeding methods to develop and test soybeans that can grow well under dry conditions. Tommy Carter started working on drought-resistant soybeans in 1981. His research has taken him as far as China, where soybeans have been grown for thousands of years. Farmers in the United States, however, have grown soybeans for only about a century. Tommy Carter says the soybeans they grow are for the most part genetically similar. More differences, or diversification, could better protect crops against climate changes that can reduce production. Those changes include water shortages which could increase from global warming. The Agriculture Department has a soy-bean germplasm collection, a collection of genetic material passed from one generation to the next. Members of Team Drought studied more than 2,500 examples from the collection. They looked at ones from the ancestral home of soybeans, Asia. They searched for germplasms that could keep plants from weakening during hot, dry summers in the United States. Tommy Carter says they found only five. But these drought-resistant lines, he says, produce four to eight bushels more than normal soybeans under drought conditions. The yield depends on location and environment.
16. What is the purpose of Tommy Carter’s research?
17. Why did Tommy Carter go to China for his soybean research?
18. What do we learn about the five germplasms Tommy Carter’s team found?