Scientists are working to develop crop p

问题：

Scientists are working to develop crop plants that can reduce the amount of water used for agriculture. Almost sixty percent of the world’s freshwater withdrawals from rivers, lakes and other water resources go toward irrigating fields.

Scientists are using biotechnology as well as traditional breeding methods to develop water-saving crops to feed a growing world.

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 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 soybean germplasm(胚质) 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 home of soybeans, Asia. They searched for germplasms that could keep plants from weakening and wilting (凋谢)during hot, dry summers in the United States.

Tommy Carter says they found only five. But these slow-wilting lines, he says, produce four to eight bushels（英斗）more than normal soybeans under drought conditions. The yield depends on location and environment.

Scientists are also working on other plants that either use less water or use it better, or both. For example, companies like Monsanto, DuPont and Syngenta have been developing corn with reduced water needs. Monsanto expects to be ready in a few years to market its first corn seeds genetically engineered to resist drought.

68. According to the passage, scientists try to find out how to _______.

A. grow crops with less water

B. increase crop production

C. feed a growing world

D. save the world’s water resource

69. Why did Tommy Carter come to China?

A. He likes traveling.

B. China has a long history.

C. He’s doing research into soybeans.

D. He works for the Agricultural Research Service.

70. What’s inferred from the passage?

A. Climate changes lead to global warming.

B. Water shortages contribute to global warming.

C. Genetically different soybeans need much water to grow.

D. Genetically different soybeans help to fight against damaging climate changes.

71. What do we know about slow-wilting plants talked about in the passage?

A. They yield big profits.

B. They can grow in almost any climate.

C. They seem to be drought-resistant.

D. They need much water for their growth.