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The research is so designed that once _______ nothing can be done to change it.

A. begins B. having begun

C. beginning D. begun

解析:

D。由于 the research 與 begin 是被動關(guān)系，故用過去分詞 begun。Once begun 可視為 once it is begun 之省略。

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科目：高中英語 來源：皇冠優(yōu)化名題　高中英語 題型：050

　　Sweet potatoes are fat-free,high in fiber and full of the vitamins that research suggests reduce your risk of life-shortening diseases．To stay healthy,we must eat more fruits and vegetables,and sweet potatoes are a great source of beta carotene（胡蘿卜素）and other carotenoids．According to a study of the diets of almost 90,000 nurses,eating about one cup a day of fruils and vegetables rich in carotenoids(which the body turns into vitamin A)can cut your risk of stroke in halt and reduce your risk of heart disease by 22 percent．Other resear chsuggests beta carotene protects against breast,lung and stomach cancers．

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This text as a whole suggests that eating sweet potatoes can help ________
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[　　]
A．	sweet potato
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The best title of this passage might be ________
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科目：高中英語 來源： 題型：053

閱讀理解：　　

閱讀下面短文，從所給四個選項(xiàng)中，選出最佳答案。

　Can trees talk? Yes——but not in words． Scientists have reason to believe that trees do communicate (互通信息) with each other． Not long ago, resear- chers learned some surprising things． First a willow tree(柳樹)attacked in the woods by caterpillars(毛毛蟲)changed the chemistry of its leaves and made them taste so terrible that the caterpillars got tired of the leaves and stopped eating them． Then even more astonishing, the tree sent out a special vapour — a signal causing its neighbours to change the chemistry of their own leaves and make them less tasty．

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