Plants have a "biological clock" that tells them when to produce leaves, seeds and other growth. A new study says understanding that clock may help scientists develop crops that can feed a growing population in an increasingly warmer world.

Rob McClung is a scientist at Dartmouth College. He says scientists need to create ways to feed the nearly 10 billion people who will be living on Earth by the middle of the century.

He says estimates show that there will need to be an increase in the world food supply of about 50 to 60 percent in the next thirty-five years.

Scientists hope that understanding how one gene affects a plant's "biological clock" will develop crops with higher yield. 

"And we're worried that the things that we've done to increase agricultural productivity（生产率） may be becoming bored."

To find new ways to increase productivity, Mr. McClung examined the biological clocks of plants. He learned that different genes in plants affect the plant's clock.

He discovered that the speed of the gene's development can affect when the plant produces. Mr. McClung says the gene also affects how the plant deals with extreme cold and high levels of salt.

"We want to be able to predict if you do this to the clock, you will do this to crop yield（生产量）."

He says he hopes his research will give plant developers a molecular（分子的） tool they can use to create a plant that can accept a higher level of salt or grow in a colder environment than usual.

Experts say the current growth in the production of the world's major food crops -- corn, rice, wheat and soybeans -- will not be enough to feed the 9.5 billion people who will be living on Earth in 2050. 

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1.In nature, plants have_____to determine their time to grow.

A leaves

B seeds

C clocks

D scientists

解析：选C。C。句子理解题。根据第1段第1句Plants have a "biological clock" that tells them when to produce leaves, seeds and other growth. 植物都有‘生物钟’来告诉它们什么时候长叶子，什么时候产种子及其他生长活动。可知答案。

2.What can people do to feed the growing population?

A Develop crops with higher yield.

B Increase the world’s food supply.

C Find the biological clock of a plant.

D Create new ways to feed people.

解析：选A。A。推理判断题。根据文章最后一段推测，只有提高粮食产量，才能养活未来更多的人，所以A答案是正确的。

3.What will the population be like by the middle of the century?

A Growing faster than now.

B Increasing by 50 to 60 percent.

C Becoming bored of food.

D Nearly 10 billion.

解析：选D。D。细节理解题。文章第2段和最后一段都提到本世纪中期，地球人口将达到的数量。

4.It is the____that plays an important part in the plant’s clock?

A productivity

B gene

C climate

D soil

解析：选B。B。细节理解题。根据文章第4段Scientists hope that understanding how one gene affects a plant's "biological clock" will develop crops with higher yield. 可知答案。

5.Which of the following statements is correct?

A The present major food crops in the world are corn, rice, wheat and soybeans.

B Now the major food crops can accept higher level of salt and cold weather.

C McClung has found the key to controlling the biological clock of crops.

D With a molecular tool, McClung can predict the yield of the crops.

解析：选A。A。细节理解题。根据文章最后一段提到的现代主要四大农作物可知。