题目

I was at the post office early that morning, hoping to be in and out in a short while. Yet, I ________ myself standing in a queue that went all the way into the hallway. I had never seen so many people there on a weekday. It seemed someone might have made an announcement, welcoming customers to carry as many ________ as they could and bring them in when I needed to have my own package _________. The queue moved very slowly. My patience ran out and I got ________. The longer it took, the angrier I became. When I got to the counter finally, I finished my __________ quickly and briefly, and then小海未将盛氢氧化钠固体试剂的瓶塞塞紧，一段时间后，它可能变质了．该反应的化学方程式为：______．所以氢氧化钠必须______保存．小海对该样品进行了系列探究：[实验方案1]：取该样品少量于试管里，加入适量的水，振荡，样品全部溶于水，再向其中滴加过量稀盐酸，观察到______说明样品真的变质了．[实验方案2]：取该样品少量于烧杯里，加适量的水，搅拌，全部溶解后，再向其中加入过量的氯化钡溶液，然后过滤，再向滤液里滴加______试液，观察到______，说明该样品是部分变质．[实验方案3]：将样品全部溶于水，向其中加入适量的______溶液除去杂质，发生反应的化学方程式为：______．