Scientists are working to develop crop plants that can reduce the amount of water used for agriculture．Almost sixty percent of the world’s fresh water taken from rivers, lakes and other water resources go toward watering fields．
Thomas Carter is a plant scientist and he leads a group of researchers．They have been using traditional methods to develop and test soybeans（大豆）that can grow well under dry conditions．Thomas started working on soybeans in 1981．His research has taken him to 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．Thomas says the soybeans they grow are genetically（基因方面）similar．More differences could protect crops against climate changes that can reduce production．Those changes include water shortages which could increase because of global warming．
Thomas and his members are working on a soybean seed collection, a collection of genetic material passed from one generation to the next．They studied more than two thousand five hundred examples from the collection which are from the home of soybeans, Asia．They searched for good seeds that could survive during hot and dry summers in the United States．Unfortunately, they found only five after a few days’ hard work．But what pleases them much is that these seeds produce four to eight ones more than normal soybeans under dry conditions．The yield（产量）depends on location and the environment．Scientists will also work on other crops that either use less water or use it better．
68．Thomas Carter and his research group do research on soybeans to     ．
A．have them survive a sharp climate change 
B．make them grow well under dry conditions
C．plant them all around the world    
D．increase crop production and quality
69．According to the passage, climate changes can     ．
A．reduce crop yield            B．protect crops
C．destroy seeds                D．change the genes of crops
70．Which of the following can be inferred from the passage?
A．Thomas and his group have made some achievements．
B．People know a little about the relationship between water and crops．
C．Seed collections depend on climate and the environment．
D．Some crops can grow well during cold and dry winters．
71．The passage is probably taken from     ．
A．a report on how to save water          B．a book on the environment
C．a science magazine                   D．an ad for agricultural products