阅读下面短文,在空白处填入1个适当的单词或括号内单词的正确形式。
Placed among the busy streets of Washington, D. C. is a large public garden that many Americans have never heard of. The U. S. National Arboretum (植物园) includes 【小题1】 collection of flowering plants called azaleas, a field of native plants named ferns, and flowering trees in the dogwood tree area. The garden 【小题2】 (establish) by Congress in 1927. It plays a leading part in researching and developing plants like trees, shrubs, flowers, and grasses.
Government scientists are in charge of the 180-hectare area. Their main goal is 【小题3】(strengthen) the U. S. economy by making sure an important kind of agriculture, 【小题4】 (call) the nursery industry, continues to perform well. The most recent numbers from the U. S. Department of Agriculture (USDA) show that the ornamental and landscape plant industry creates billions of founds in sales each year.
The arboretum is home to one of the 【小题5】 (large) collections of preserved seeds in the world. The National Arboretum Herbarium (植物标本) 【小题6】 (house) around 700,000 ex-ample seeds. They include seeds from plants that the USDA considers as 【小题7】(economical) important. Scientists collect many genetically different seeds within a kind of plant from both native and non-native plants. The reason 【小题8】 collecting that data is that scientists protect plants from harmful situations like climate change, changed environments, or other new and possible risks.
While the scientists do their work, the public 【小题9】 (explore) plants is free to visit the arboretum. Though many people may not know it, the arboretum has had a hand in developing a number of plants 【小题10】 are part of American landscaping.