①取一定量该样品放入烧杯中并加入足量水搅拌后，样品全部溶解且得到无色溶液；

②向无色溶液中加入过量的 CaCl₂ 溶液充分反应，出现白色沉淀，将白色沉淀经过滤、洗涤、干燥、称量。根据上述实验现象回答：

如图，在⊙O中，弦AD=弦DC，则图中相等的圆周角的对数是（      ）

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    Hello! I'm Wang Lin. I like sports very much. Basketball is 1 favourite sport. Tom is my friend. He is an 2  boy. He is from America. He is 12 3  old. He likes sports, too. He has（有）a big ball collection（收藏物） 4  his room. There are 5  balls in the room. Tom's  6  aren't at home.  7  his sister Dee is at home. She is in the room now. Her favourite 8  is football. I don't like  9  because（因为）she isn't nice to me. I want（想要）to have a 10 collection too. Then I can have many balls. Do you want to have one?