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问题 选择题

癌症是严重威胁人类健康的疾病之一。引起细胞癌变的内在因素是[ ]

A．细胞中酪氨酸酶活性降低

B．致癌因子激活原癌基因

C．长期受到电离辐射或X射线照射

D．霉变或熏制食物中所含有的致癌物质

答案

答案：B

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Dear Christie，

I’m here in the National Park, in     （southeast）California.                           72.    

I have been t    around the state of California for three weeks                                   73.    

now, It's very different from        I have seen in American movies.                         74.    

Not everyone is rich and not everyone l     near the beach. I first                             75.    

travelled southeast      rich farmland then to the central part.                                    76.    

They grow e     here including cotton，vegetables，nuts and                                   77.    

fruit．They raise cattle too．Then I traveled   （far）southeast into                          78.    

mountains and desert. Californians are very friendly,      they are                              79.    

from many different r    and cultures. Every cuIture has its own                              80.      ，

music，food and art. I show great interest in them．                                                   81.    

Wish you were here. Give my love to Paula.

Yours，

           George
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问答题 简答题

汽轮机蒸汽流量的变化对轴向推力有什么影响？
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