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问题 选择题

2009年4月29日从公安部获悉，为回应群众要求，快速、高效地查找被拐卖儿童，公安部已建成全国“打拐”DNA数据库，用信息成果和高科技手段查找被拐卖儿童，DNA主要从细胞哪一结构提取（　　）

A．细胞壁

B．细胞质

C．细胞膜

D．细胞核

答案

细胞核在生物遗传中具有重要作用，细胞核中容易被碱性染料染成深色的是染色体，它是由DNA和蛋白质组成的，DNA是主要的遗传物质．细胞壁具有支持保护细胞的作用．细胞膜具有保护细胞内部的作用，还能控制细胞内外物质的进出．活细胞的细胞质具有流动性，有利于细胞与外界环境之间进行物质交换．因此，选项A、B、C均不符合题意．

故选：D

单项选择题

沥青混合料车辙试验的评价指标为( )。

A．稳定度

B．残留稳定度

C．动稳定度

D．残留强度比
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单项选择题

There is virtually no limit to how one can serve community interests, from spending a few hours a week with some charitable organization to practically full-time work for a social agency. Just as there are opportunities for voluntary service (1) (VSO) for young people before they take up full-time employment, (2) there are opportunities for overseas service for (3) technicians in developing countries. Some people, (4) those who retire early, (5) their technical and business skills in countries (6) there is a special need.

So in considering voluntary or (7) community service, there are more opportunities than there (8) were when one first began work. Most voluntary organizations have only a small full-time

(9) and depend very much on volunteers and part-timers. This means that working relationships are different from those in commercial organizations, and values may be different. (10) some ways they may seem more casual and less efficient, but one should not (11) them by commercial criteria. The people who work with them do so for different reasons and with different (12) , both personal and (13) . One should not join them (14) to arm them with professional experience; they must be joined with commitment to the (15) , not business efficiency. Because salaries are (16) or non-existent many voluntary bodies offer modest expense. But many retired people take part in community service for (17) , simply because they enjoy the work.

Many community activities possible (18) retirement were also possible during one’s working life but they are to be undertaken (19) seriously for that. Retired people who are just looking for something different or unusual to do should not consider (20) community service.

20（）

A. to be taken

B. to take

C. taking

D. being taken
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