Gamma rays used to irradiate food ___.A.are generally not strong enough to destroy contami

nirradiated food. Since the 1960’s researchers have studied irradiated food at microscopic levels to try to find such substances, called unique radiolytic products. After reviewing these studies, the FDA determined that compounds formed during irradiation are similar to substance found in nonirradiated foods and are not dangerous to consume. Destruction of microorganisms that cause illness is an important goal of irradiation. About 250 million cases of food poisoning or 1 per person—occur every year in the U.S., according to FDA estimates. Food poisoning can cause vomiting, diarrhea, fever, headache—and, occasionally, death. Because of the apparent safety of food irradiation, and the problems presented by contaminated food, scientific groups—including the American Medical Association, the World Health Organization, and the United Nations food and Agriculture Association—have voiced nearly universal support for the process. Worldwide, 38 nations have approved irradiation for 355 products. Like microwave ovens, food irradiation has aroused apprehension and misunderstanding. Yet it has been scrutinized more thoroughly than other methods of food treatment that we have come to regard as safe, and it appears to be a method whose time has come. Cobalt 60, besides irradiating food, is also employed to ___.

A.detect metallic flaws

B.run a nuclear reactor

C.cure cancer patients

D.strengthen concrete walls

Scientists perform careful experiments and do wide research because______.

A.they must learn to destroy all the insects that we need

B.they must be sure one insect pest is not traded for another

C.research keeps them from inventing new insecticide for the crops

D.research helps them find a way to kill all insects

Which statement does this article lead you to believe?

A.All changes are predictable.

B.Nothing ever changes in nature.

C.Nature is not always predictable.

D.Nature always serves man well.

On the whole, the article tells about______.

A.the appetites of plant-eating insects

B.the best way to kill boll weevils

C.the dangers in using insecticides

D.the best way to grow crops

While it is not directly stated, the article suggests that______.

A.insecticides are not dangerous to any small animals

B.insecticides do not always accomplish their purposes

C.insecticides are no longer being used to kill insects

D.insecticides do no harm to people

ve damaged them. Between 1870 and 1880, locusts ate millions of dollars' worth of crops in the Mississippi Valley. Today in the United States the cotton boll weevil damages about 300 million dollars' worth of crops each year. Additional millions are lost each year to the appetites of other plant-eating insects. Some of these are corn borers, gypsy moths, potato beetles, and Japanese beetles. In modern times, many powerful insecticides(杀虫剂) have been used in an attempt to destroy insects that damage crops and trees. Some kinds of insecticides, when carefully used, have worked well. Yet the same insecticides have caused some unexpected problems. In one large area, an insecticide was used against Japanese beetles, which eat almost any kind of flower or leaf. Shortly afterward, the number of corn borers almost doubled. As intended, the insecticide had killed many Japanese beetles. But it had killed many of the insect enemies of the corn borer as well. In another case, an insecticide was used in Louisiana to kill the troublesome fire ant. The insecticide did not kill many fire ants. It did kill several small animals. It also killed some insect enemies of the sugarcane borer, a much more destructive pest than the fire ants. As a result, the number of sugarcane borers increased and severely damaged the sugarcane crop. To be sure that one insect pest will not be traded for another when an insecticide is used, scientists must perform careful experiments and do wide research. The experiments and research provide knowledge of the possible hazards an insecticide may bring to plant and animal communities. Without such knowledge, we have found that nature sometimes responds to insecticides in unexpected ways. An insecticide was used in Louisiana to kill the troublesome______.

A.corn borer

B.Japanese beetle

C.gypsy moth

D.fire ant

othing they can do about their illness.

此题为判断题(对，错)。