题目

阅读理解In the age of online shopping and e-readers,devoted staff and customers keep the doors of Auntie's Bookstore open for 40 years.When you're in Portland, you go to Powell's Books. When you're in Seattle,you go to Elliott Bay. When you're in Spokane, you go to Auntie's, said JohnWaite, the owner of the bookstore. I can't imagine Spokane without Auntie's,he said. A lot of people can't imagine Spokane without Auntie's, either,Waite said.Turning visitors into regular customersis important to the store's success. Auntie's markets itself as a destination. Ahalf-dozen book clubs meet there.现有下列七种物质：①部分结冰的蒸馏水；②铁；③空气中分离出来的稀有气体；④过氧化氢；⑤湖水；⑥高锰酸钾加热制氧气后的剩余物；⑦一种黑色的固体粉末，其中肯定属于混合物的有（填序号，下同）    ，肯定属于纯净物的有    ．