5 . The worldwide 20th century “Green Revolution”, which saw huge year-by-year increases in global grain yields (产量),was fueled by the development in the 1960s of new high-yielding dwarfed (矮小) varieties known as Green Revolution Varieties (GRVs).

These dwarfed GRVs are common all over the world in today’s wheat and rice crops. Because they are dwarfed, with short stems, GRVs devote relatively more resources than tall plants to the growth of grains rather than stems, and are less likely to suffer yield losses from wind and rain damage. However, the growth of GRVs requires farmers to use large amounts of nitrogen fertilizers (氮肥) in their fields. These fertilizers are costly to farmers and cause extensive damage to the natural environment. The development of new GRVs combining high yields with reduced fertilizer requirements is thus a global agricultural goal.

Researchers at the University of Oxford and the Chinese Academy of Science have discovered for the first time a gene that can help reach the goal. Comparing 36 different dwarfed rice varieties, the researchers identified a novel natural gene that helps increase the rate at which plants make use of nitrogen from the soil. This gene, called GRF4, can increase the amount of a protein (蛋白质) in plant cells. GRF4 is actually a promoter that encourages the activity of other genes—genes that promote nitrogen uptake (摄入). Professor Harberd said, “Increasing GRF4 levels could contribute to an increase in the grain yields of GRVs, especially at low fertilizer input levels.”

The researchers say the latest rice variety containing GRVs should now become a major target for farmers in increasing crop yields and fertilizer use efficiency, with the aim of achieving the global grain yield increases necessary to feed a growing world population at a reduced environmental cost. It is very urgent at the moment.

Professor Harberd added, “This study is an example of how studying fundamental science objectives can lead rapidly to potential solutions to global challenges. It shows how the discovery can enable chances for food security and future new green revolutions.”

1. What can we know about dwarfed GRVs?

A．They have higher yield and taller stems.

B．They are a “double-edged sword”.

C．They are environmentally friendly.

D．They can be easily affected by weather.

2. What does “the goal” in Paragraph 3 refer to?

A．Increasing the rate of nitrogen use.

B．Producing cheaper nitrogen fertilizers.

C．Using fewer fertilizers to produce more grains.

D．Finding a gene to solve agricultural problems.

3. What can GRF4 directly do?

A．It promotes other genes' activity.

B．It increases the output of crops.

C．It takes in nitrogen from the soil.

D．It lowers fertilizer input levels.

4. What’s the urgent thing recently according to the researchers?

A．Decreasing the amount of fertilizers required by GRVs.

B．Encouraging farmers to adopt the new rice variety.

C．Calling on farmers to use effective fertilizers.

D．Focusing on the improvement of GRF4.

5. What’s the main idea of the text?

A．GRVs—a potential measure to achieve global food security.

B．The influence of agricultural development on the environment.

C．The importance of raising public awareness of global issues.

D．GRF4—foundation for new green revolutions.