区别下列各组物质的方法可行的是
A．用稀盐酸区分氢氧化钠溶液和澄清石灰水
B．用稀硫酸区分木炭粉和氧化铜粉末
C．用蒸馏水区别四氧化三铁粉末和铁粉
D．用铜片区别稀盐酸和稀硫酸
B
题目分析：A．稀盐酸与氢氧化钠溶液、澄清石灰水均发生反应且无明显变化，无法区分。此项不正确。 B．稀硫酸有与木炭粉反应，无明显变化；稀硫酸可与氧化铜粉末反应，观察到粉末溶解，溶液变为蓝色。可区分二者。此项正确。C．四氧化三铁粉末和铁粉均不溶解于蒸馏水，无法区别。此项不正确。D．铜片与稀盐酸、稀硫酸均不反应。无明显变化，无法区分。此项不正确。所以应选B项。
Everybody wants a new start for a new school year. So, students often go back-to-school shopping. They buy school things and shoes. But, the story is not so easy. "Mum, I want this pair of shoes!" "Dear! Those are 900 yuan! That is too __16___ !" "But all the boys in my class wear this brand (牌子)!" So the real story is: Kids___17____to catch up with school fashion. Chinese students __18__ uniforms at school. Parents think all the kids look the same, but kids know the differences. The "rich" kids wear amazing watches, ride good 19__and use cool pencil cases. They show off their expensive things to 20__ kids. Then everyone else wants them too. For example, some "rich" kids use a pencil box that _21_1,000 yuan! It not only holds pencils, but also has a thermometer (温度计), a compass (指南针), a music box and even games in it! But think about it. Do you really need ____22___ a special pencil box? What can you do with a compass or a thermometer in class? They only distract (分散注意) you. As for these "rich" kids, they are not rich at all. 23__ parents buy them all their school things. They may have an advantage now, but it won’t last forever. If you want to show off __24__ money you have, you have to make it yourself first. So, study hard. You will get a great job in the future. Parents should also learn __25___to refuse their kids’ demands (要求). They should tell their kids: as students, what is really important is not school fashion but good school grades.
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