在元素周期表主族元素中。甲元素与乙、丙、丁三元素紧密相邻。甲、乙的原子序数之和等于丙的原子序数。这四种元素原子的最外层电子数之和为20。下列判断正确的是
A．原子半径：丙>乙>甲>丁
B．丁或甲与乙所形成的化合物都是有毒的物质
C．最高价氧化物的对应水化物的酸性：丁>甲
D．气态氢化物的稳定性：甲>丙
答案：D
根据题意要求知甲为原子序数为7的氮元素，乙为氧元素，丙为磷元素，则丁为碳元素。A项原子半径丙>丁>甲>乙；B项，乙和丁形成的CO2不是大气污染物；C项，最高价氧化物对应水化物的酸性甲>丁；D项，气态氢化物的稳定性甲>丙，故选D。
第二节任务型阅读（共10小题；每小题1分，满分10分） 请认真阅读下列短文，并根据所读内容在文章后表格中的空格里填入最恰当的单词。 注意：每空格1个单词。 When we think about education and language learning, we are most likely to think of books. Although there are lots of language learning methods, many people still prefer to learn only by using books. So what are the advantages of learning a language from a book? Here are its advantages: firstly, you can take language books wherever you go conveniently and you can use them whenever you want. Secondly, they are easy to follow because the courses in them are usually planned for you in strict order starting from the most basic concepts to the more complex. Thirdly, if you are unsure of something, you can continue to work on it as quickly as you like. Lastly, books are likely to have a lot of vocabulary and a lot of topics so you will get great value out of a book with lots of materials in it. Using books to study a language has disadvantages, too. All textbooks and dictionaries usually include some kind of pronunciation guide. These are helpful when there is no other way to learn, but this can't help you practice your pronunciation. With an audio method, you can compare your pronunciation to that of a native speaker. Besides, some words are spoken faster in one sentence or slower in another, so the pronunciation of a word may change according to the emotion or feeling you want to convey. Also, books can’t actually help you hear the language with its unique rhythms spoken by native speakers. With an audio language learning method, you will be able to hear and understand the language better. Therefore, if you can supplemental（补充）your book with some other language tools, such as audio tapes, internet radio or resources such as music or television, you will have a much better chance of understanding the books' pronunciation guide and using it to get a good grasp of the spoken language.
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