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教师都要用粉笔写字,怎样才能使粉笔不脏手呢?国外有人这样处理粉笔,使之既不影响板书,也不会把手弄脏:将颗粒状的聚乙烯醇缩醛(一
Teachers should use chalk to write, how to make the chalk dirty hand? Some people abroad so dealt with chalk, so that it does not affect the blackboard, it will not dirty hands: the granular polyvinyl acetal (a