A. Because many old people are changing their professions. B. Because some people are looking for better jobs. C. Because they have high costs for repairs and advanced technology. D. All of the abov
参考答案:D 答案解析:通过原文“One reason for this is that many older people are changing their professions.They are looking f
第32题: [单项选择]水中铜的测定方法是()。 A. 水杨基荧光酮氯代十六烷基吡啶分光光度法 B. 二氮杂菲分光光度法 C. 过硫酸铵分光光度法 D. 双乙醛草酰二腙分光光度法 E. 二乙氨基二硫代甲酸银分光光度法 参考答案:D 答案解析:1.在硝酸银存在下,锰被过硫酸铵氧化成紫红色的高锰酸盐,其颜色的深度与锰的含量成正比。
2.水中的铝离子与水杨基荧光酮及阳离子表面活性剂氯代十六烷基吡啶在pH5.2~6.8范围内形成玫瑰红色三元络合