A:白醋和白酒 (观察颜色)
B:水与双氧水(取样,加少量二氧化锰)
C:二氧化碳与氮气(燃着的木条)
D:食盐与蔗糖(闻气味)
读课文《詹天佑》说说詹天佑在修筑铁路时遇到了哪些困难?
A. fold the clothes B. sweep the floor
C. make your bed D. take out the rubbish
E.do the dishes
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