搜题请搜索小程序“爱下问搜题”
问题 不定项选择题

某兴趣小组设计实验探究碳酸钠、碳酸氢钠与盐酸反应过程中的放、吸热情况。操作步骤为：①向试剂1中加入试剂2，搅拌、测温；②静置、测温；③再加入试剂3，搅拌、测温、记录。得到了如下数据：

则下列说法中，错误的是[ ]

A. Na2CO3在溶于水的过程中放出热量

B. NaHCO3在溶于水的过程中吸收热量

C. 其它条件相同时，碳酸氢钠溶液与盐酸混合过程中放出的热量更多

D. 实验中，若同一列试剂的温度及所取的量不同，则实验结论的可信度降低

答案

答案：C

选择题

如图所示，小球从斜面上某一高度由静止开始滑下，撞击静止于水平木板上的木块（不计空气阻力），下列说法正确的是

A．小球在斜面上下滑的过程中，如果以木板为参照物，小球是静止的

B．若木板的表面光滑且足够长，最终木块的动能保持不变

C．木块对木板的压力就是木块的重力

D．小球从斜面上开始下滑到撞击木块后静止的过程中，小球的机械能先变大后变小
查看答案
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.

15（）

A.course

B.cause

C.case

D.caution
查看答案