题目

Children do not think the way adults do. For most of   61   first year of life, if something is out of sight, it is out of mind.   62   you cover a baby’s favorite toy with a piece of cloth, the baby thinks the toy has disappeared and stops   63   (look) for it. A 4-year-old may object that his/her sister has   64  (much) fruit juice when it is only the shapes of the glasses that differ, not the amount of juice.        Yet children are smart   65   their own way. Like good little scientists, children are always testing their child-sized theories about   6某白色固体由CuSO4、MgCl2、CaCl2、NaOH、Na2CO3中的三种物质组成，为确定其成分，相关实验及现象如下（微溶性物质按可溶处理）：综合分析上述实验，回答下列问题：（1）原白色固体中一定没有的物质是　 ；（2）无色溶液a中一定含有的溶质是　 　；（3）原白色固体中只有一种物质没有确定其是否存在，要确定其是否存在，还需补充的实验是　 　．