题目

有两瓶失去标签的氯化钙溶液和稀硫酸溶液，现要用一种试剂鉴别它们，下列试剂可行的是      A．稀盐酸      B．碳酸钠溶液     C．无色酚酞试液     D．         答案：【答案】B  石磊溶液  等 【解析】加入碳酸钠，生成白色沉淀的就是氯化钙，有气泡生成的就是稀硫酸，故可以选B，盐酸与氯化钙和稀硫酸都不反应，氯化钙显中性，稀硫酸显酸性，酚酞加入后都不变色，故A、C都不可以，还可以用石蕊，加入后，会变红的是硫酸，不变色的是氯化钙。Have you ever asked yourself why children go to school? You will 小题1: (probable) say that they go to learn languages，arithmetic，history, science and some other knowledge．That is quite true；but why do they learn these things? We send our children to school to prepare them for the time   小题2: they will be big and will have to work for 小题3: ．Nearly everything they study at school has some practical use in their life．But is that   小题4: only reason why they go to school? There is more in education than just 小题5:(1earn)facts．We go to school to learn how to learn，so that when we have left school we can continue to learn．A man 小题6:  really knows how to learn will always be successful，because when he has to do something new, he will not only be able to do it well himself, he will also be able to teach others  小题7:  to do it in the best way．The 小题8:  (educate)person，on the other hand，is either unable to do something new，or just 小题9: (do) it badly．The purpose of schools，therefore，is not to teach languages，arithmetic，history science，etc．，  小题10: to teach pupils the way to 1eam．