题目

短文填空。阅读下面材料，在空白处填入适当的内容（不多于3个单词）或括号内单词的正确形式。 Mr. Johnson lived in the woods with his wife and children. He owned farm, which looked almost abandoned. (lucky), he also had a cow which produced milk every day. He sold or exchanged some of the milk in the towns nearly for other food and made cheese and butter for the family with what (leave). The cow was their only means of support, in fact. One day, the cow was eating grass it began to rain heavily. While (make) great efforts to run away, she (fall) over 氢氧化钠是一种重要的化工原料．氢氧化钠溶液长期暴露在空气中会逐渐变质，检验氢氧化钠溶液是否变质的试剂是______，若已变质，则检验时可观察到的现象是______．