题目内容：

Benefits and Problems of Genetic Engineering

Plant breeding is the science of changing the characteristics of plants in order to produce desired ones. Genes in a plant are what determine what type of characteristics it will have. Plant breeders try to create a specific outcome of plants and potentially new plant varieties by changing the genes of the plants through breeding, which is making new plants from parents of different varieties or species.

Actually, plant breeding has been practiced for thousands of years, since near the beginning of human civilization. It is practiced worldwide by individuals such as gardeners and farmers and by professional plant breeders employed by organizations such as government institutions, universities, crop-specific industry associations or research centers. They have crossbred plants to create the new types of plants that are, for example, bigger, stronger, or more attractive.

Crossbreeding can take such a long time, however, and it is inaccurate. Now, we can change exact sections of Deoxyribonucleic acid (DNA), so the process is more accurate and faster. But people all over the world are arguing about its benefits and disadvantages. Some people use the technology to produce desired characteristics of plants and animals. Other people are concerned that the genetically engineered plants may harm the environment and worried that they may be dangerous for people to eat.

There are many reasons for changing plants in this way. International development agencies believe that breeding new crops is important for ensuring food security by developing new varieties that are higher yielding(高产的), disease resistant, drought tolerant or regionally adapted to different environments and growing conditions. For example, some genetically engineered plants can live through frost or draught. As a result, famers can make more profit because fewer plants will die.

Some genetically engineered plants are more nutritious. They have less fat, taste better or stay fresher than non-genetically engineered plants. This will allow people to buy better-quality fruit and vegetables.

Some genetically engineered plants can resist natural pests such as viruses or insects. This reduces the amount of chemical needed to kill pests, which is helpful to the environment.

However, genetically engineered plants can cause unexpected problems. Genetically engineered plants that resist pests may pass on that characteristic to a wild relative. This may cause the wild plant to spread fast, because pests are not naturally killing it.

Genetically engineered plants can also harm animals. A type of corn has been developed which kills a species of insect that destroys it. The pollen (花粉) from this corn, however, can also kill monarch butterflies—the most beautiful of all butterflies, which do not harm the corn.

To ensure the most adapted varieties are identified, advocates of organic breeding now promote the use of direct selection for many desired characteristics.

Genetic engineering is a very new science and we have a lot to learn about the good it can do and the damage it can cause. The main concern is that not enough tests are being done to ensure it is safe.

1.According to the passage, the purpose of plant breeding is to _______.

A.beautify the environment B.change the genes of plants

C.produce new plant varieties D.assess the value of the practice

2.The author thinks crossbreeding inaccurate because _______.

A.the sections of DNA are changed

B.problems are sometimes caused

C.manpower and resources are wasted

D.animals are produced using the technology

3.The author’s attitude toward crossbreeding is _______.

A.doubtful B.disapproving

C.objective D.supportive

4.Which of the following best shows the structure of the passage?

Sp：Sub-point （次要点）      C：Conclusion

I：Introduction       Cp：Central Point       P：Point

A. B.

C. D.