2、Rice plants normally grow well in still water. But most will die if they are completely underwater for more than four days. Now, researchers have identified a gene (基因) that helps rice survive longer underwater. They say the discovery will lead to new kinds of rice plants that can survive flooding, and therefore reach their final aim, ensuring more dependable food supplies.

Tests are now being done in Laos, Bangladesh and India. The researchers say experimental rice plants with the gene have survived underwater as long as two weeks. When flooding happens, most kinds of rice plants cannot get enough oxygen, carbon dioxide or sunlight. But the scientists say crop loss depends on several conditions. These include soil conditions and plant age. Others include the amount of time the plant is underwater and the amount of fertilizer (肥料) used on the crop.

On a genetic (遺傳的) map of rice, the scientists became interested in a group of three genes. They experimented with one of them, a gene known as Sub-One-A. They found that when this gene becomes very active, it improves the ability of rice to survive longer when rice is covered by water. They believe it succeeds because it affects the reaction to hormones (荷爾蒙). They control the ability of a flooded plant to survive. Placing the gene into rice plants that are especially good for conditions in India, researchers say the genetically engineered plants not only survived but also produced good crops.

The researchers are now trying to identify all the genes governed by the Sub-One-A gene. Being able to leave water on rice plants for an additional week might also help farmers prevent the growth of weeds. Less weed growth around their crops would mean less need for herbicide (除草劑) chemicals.

 

41. Crop loss depends on all the following conditions EXCEPT _______.

A. soil conditions and plant age

B. the amount of water the plant stands in

C. the amount of fertilizer used on the crop

D. the amount of time the plant is underwater

42. What is the final aim of this research?

A. To identify the gene that helps rice survive underwater.

B. To increase the ability of rice to fight against floods.

C. To help farmers spend less time removing weeds.

D. To make sure of enough food supplies.

43. What does the underlined word “They” in Paragraph 3 refer to?

A. Genes.                                             B. The experiments.

C. Genetically engineered plants.             D. Hormones.  

44. What would be the best title for the passage?

A. Rice research is going on in Laos and India

B. How to reduce the influence of floods on rice

C. Gene researchers work on flood-resistant rice

D. A great discovery in the agricultural field