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问题 计算题

有一种新型火箭燃料化学式为N(NO2)3，则

（1）它的相对分子质量为    ，其中氧元素与氮元素的质量比为    。

（2）N(NO2)3中氮元素的质量分数是多少？(列式计算    )

（3）N(NO2)3中含有氮元素的质量是多少？(列式计算    )

答案

（1）152   12：7

（2）×100%=36.84%

（3）30kg×36.84%="11" kg

题目分析：

（1）相对分子质量是相对原子质量之和。它的相对分子质量为14×4+16×6=152。氧元素与氮元素两种元素的元素质量比为16×6：14×4=96：64=12：7

（2）氮元素质量分数是指化学式中氮元素质量占整个分子质量的百分数。故列式如上。

（3）30kg N(NO2)3中含有氮元素的质量只需将30kg乘以N(NO2)3中氮元素的质量分数即得答案。

单项选择题

When I first entered university, my aunt, who is an English professor, gave me a new English dictionary. I was (16) to see that it was an English-English dictionary, also known as a monolin-gual dictionary. (17) it was a dictionary intended for non—native learners, none of my classmates had one (18) , to be honest, I found it extremely (19) to use at first. I would look up words in the dictionary and (20) not fully understand the meaning, I was used to the (21) bilingual dic-tionaries, in which the words are (22) both in English and Chinese, I really wondered why my aunt (23) to make things so difficult for me. Now, after studying English at university for three years, I (24) that monolingual dictionaries are (25) in learning a foreign language.

As I found out, there is (26) often NO perfect equivalence(对应) between two (27) in two language. My aunt even goes so far as to (28) that a Chinese "equivalent" can never give you the (29) meaning of a word in English! (30) , she insisted that I read the definition(定义) of a word in a monolingual dictionary (31) I wanted to get a better understanding of its meaning. (32) , I have come to see what she meant.

Using a monolingual dictionary for learners has helped me in another important way. This dictionary uses a(n) (33) number of words, around 2,000, in its definitions. When I read these definitions, I am (34) exposed to (接触)the basic words and learn how they are used to explain objects and ideas. (35) this, I can express myself more easily in English.

27（）

A. words

B. names

C. ideas

D. characters
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判断题

川乌头、草乌头、雪上一枝蒿等含乌头碱，对心脏有毒性。（）
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