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nn9219812
2 năm trước
They first met ten years ago.




A.They had a meeting ten years ago.
B.The first time they met was ten years ago.
C.They have known each other for ten years.
D.Both b and c are correct.
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Các câu hỏi liên quan

I. Read the passage carefully and choose the correct answer.
Plants and animals hold medicinal, agricultural, ecological value. Endangered species must be protected and saved so that future generations can experience their presence and value.
Plants and animals are responsible for a variety of useful medications. In fact, about forty percent of all prescriptions written today are composed from the natural compounds of different species. These species not only save lives, but they contribute to a prospering pharmaceutical industry worth over $40 billion annually. Unfortunately, only 5% of known plant species have been screened for their medicinal values, although we continue to lose up to 100 species daily. The Pacific yew, a slow-growing tree found in the ancient forests of the Pacific Northwest, was historically considered a "trash" tree. However, a substance in its bark was recently identified as one of the most promising treatments for ovarian and breast cancer. Additionally, more than 3 million American heart disease sufferers would die within 72 hours of a heart attack without digitalis, a drug derived from the purple foxglove.
There are an estimated 80,000 edible plants in the world. Humans depend upon only 20 species of these plants, such as wheat and corn, to provide 90% of the world's food. Wild relatives of these common crops contain essential disease-resistant material. They also provide humans with the means to develop new crops that can grow in inadequate lands such as in poor soils or drought-stricken areas to help solve the world hunger problem. In the 1970s, genetic material from a wild corn species in Mexico was used to stop a leaf fungus that had previously wiped out 15% of the U.S. corn crop.
Plant and animal species are the foundation of healthy ecosystems. Humans depend on ecosystems such as coastal estuaries, prairie grasslands, and ancient forests to purify their air, clean their water, and supply them with food. When species become endangered, it is an indicator that the health of these vital ecosystems is beginning to unravel. The U.S. Fish and Wildlife Service estimates that losing one plant species can trigger the loss of up to 30 other insect, plant and higher animal species. The northern spotted owl, listed as threatened in 1990, is an indicator of the declining health of the ancient forests of the Pacific Northwest. These forests are the home to over 100 other old-growth dependent species, which are at risk due to decades of unsustainable forest management practices. Pollution off the coast of Florida is killing the coral reefs along the Florida Keys, which serve as habitat for hundreds of species of fish. Commercial fish species have begun to decline, causing a threat to the multi-million dollar tourism industry, which depends on the quality of the environment.
According to the text, _______.




A.there is no disease-resistant material in edible plants
B.human beings depend on plants for food and medicine
C.human beings do not like to use plants as medicine
D.edible plants do not include wheat and corn

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