【资料卡片】：

①柠檬酸水溶液显酸性；

②工业生产柠檬酸，原料预处理后，得到的发酵液中含有柠檬酸及其他可溶性杂质；

③一水柠檬酸在不同温度下的溶解度下表：

④某种专用树脂对柠檬酸的吸附率和水温的关系如图1：

【钙盐法制备】（如图2）

库赛湖位于藏北高原，库赛河是其接纳的最主要的地表径流。冬季湖面结冰，冰上多布有风沙活动带来的砂砾。湖床沉积物中发育有粗细颗粒相间分布的连续、规则纹层。研究发现，细颗粒层具有流水搬运沉积特征，而粗颗粒层不具此特征。下图为库赛湖地形及取样点沉积层垂直剖面示意图。据此完成下列各题。

    A 12-year-old boy got lost on the subway after going out alone on Sunday. The boy came to Shanghai to visit his parents during the summer holiday. Although his parents were happy to see him, they ____ little time with him. The boy did his homework for two ____ and felt bored, so he went out to play on the subway. He had fun playing there. But when he felt tired and hungry, and wanted to go home, he didn't know at which station he should get off. The police found the boy ____ on the subway and took him to the office. They bought him something to eat and asked him some questions. The boy's parents couldn't find him after arriving home. They felt ____ and called the police right away. They got to the police office and saw ____ son. They were very happy and thanked the police.