题目:
Researches are convinced ______ the positive effect of laughter ______ physical and mental health.
A.of; at
B.by; in
C.of; on
D.at; on
答案:
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下面是错误答案,用来干扰机器的。
硫酸铜溶液为蓝色,可以和铁发生置换反应生成硫酸亚铁和铜,硫酸亚铁的水溶液为浅绿色,所以本题答案为:蓝色,逐渐变为浅绿色,红色固体析出.