根据语篇情景，用恰当的短语或句子填空，使之意思完整。

Class Nine 1.________________________ on the school trip. They went to Blue Water Aquarium for the day. First they visited the Visitors’ Center and watched a movie about sharks. Then they watched a dolphin show. After that, they went to the Outdoor Pool and saw a big octopus. After lunch, they went to the Gift Shop and 2.____________________________. Finally, tired but happy, they took the bus back to school. At the end of the day, the science teacher 3. __________________ because the class monitor cleaned the bus after the trip.

现欲探究一固体混合物A的成分，已知其中可能含有NaNO₃、NH₄Cl、CuO、Fe、Cu（OH）₂、MgSO₄六种物质中的两种或多种．按如图所示进行实验，出现的现象如图中所述（设过程中所有可能发生的反应都恰好完全反应）．

试根据实验过程和发生的现象填写以下空白：

（1）气体D能使湿润的红色石蕊试纸变为　    　色．

（2）固体H的化学式是　    　．

（3）溶液F中一定含有的酸根离子有（写离子符号）　            　．

（4）根据步骤②你能确定混合物中一定存在的一种物质是　        　（只写一种，填化学式），你判断的依据是　                                  　．

（5）步骤②中生成白色沉淀E的有关反应的化学方程式　                           　．