可供试剂a、b的选择试剂：饱和Na₂CO₃溶液、饱和K₂CO₃溶液、KOH溶液、BaCl₂溶液、Ba（NO₃）₂溶液、H₂O₂、KMnO₄（H⁺）溶液、稀HNO₃．

请根据以上流程，回答相关问题：

    A new study says that American children have exciting after-school life. Many junior and senior students have a lot of interesting things to do in their free time. About 57% students have activities every day. 82% students have activities at least four times a week. American students spend their free time doing sports or enjoying arts, music and dancing. They like to have fun outside school because they can make a lot of friends during their activities.

中国第２７次南极科学考察队于2012年12月５日顺利抵达南极中山站。我国科学考察队去南极考察一般在11—12月抵达南极洲，主要原因是（   ）