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问题 填空题

已知数列{an}是等差数列，a2=8，a8=26，从{an}中依次取出第3项，第9项，第27项，…，第3n项，按原来的顺序构成一个新数列{bn}，则bn=（    ）．

答案

3×3n+2

填空题

用动词的适当形式填空。

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4. There ________ (be) a football match this evening.

5. Please tell us when ________ (begin) as soon as you have the news.

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问答题 简答题

润滑油的三级过滤指哪三级？
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