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问题 单项选择题

癌与肉瘤的主要区别是（）。

A.发生的部位不同

B.肿瘤的颜色不同

C.肿瘤的质地不同

D.发生的年龄不同

E.组织来源不同

答案

参考答案：E

解析：癌和肉瘤的主要区别是癌是上皮来源的，而肉瘤是间叶组织来源的。

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短文填空 根据短文内容及首字母提示，补全空格内单词，使短文完整通顺。（10分）

In the USA, children between the ages of 8 and 14 are a powerful group. They make up 60% of Internet users u  小题1:  age18. Just as in America, the number of teen Internet users in China is g 小题2: bigger, up to 253 million. The number shows a great increase in Internet use in China over the last f 小题3: years, particularly among teenagers, and China becomes a large m  小题4:for Internet business.

A new survey r  小题5:  that Chinese teens take an interest in online activities. And spending too much time before a computer screen causes a lot of p  小题6:for their young life. According to the survey, 42.6% of teens have built their o  小题7:web blogs and 8% have taken Internet courses. More than half enjoy c  小题8:online in chat-rooms and 10.6% of teens play Internet games. In the eyes of most parents, what a p  小题9: that only 6% use the Internet to get information for their learning projects! Also, the survey finds that the teens have different favourite places to use the Internet. For teens in towns, 35% c  小题10:  Internet bars as a main place to go online. For those living in large cities, 76% prefer home computers and 10% Internet bars.
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选择题

牛肉中亚硝酸盐的含量应小于30mg/Kg．人若食用亚硝酸钠（NaNO2）超标的牛肉，轻者嘴唇、手指甲发紫；重者中毒，甚至死亡．关于NaNO2的叙述不正确的是（　　）

A．N元素的化合价为+5价

B．Na、N、O元素的质量比为23：14：32

C．NaNO2的相对分子质量为69

D．N元素的质量分数约为20.3%
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