甲、乙、丙、丁分别是Al₂(SO₄)₃、FeSO₄、NaOH、BaCl₂四种物质中的一种，若将丁溶液滴入乙溶液中，发现有白色沉淀生成，片刻沉淀由白色变为灰绿色又变为红褐色；将丁溶液滴入甲溶液，有白色沉淀生成，而将甲溶液滴入丁溶液时，无沉淀生成，据此可推断丙物质是(　)

    The ant(蚂蚁) works every day but the monkey plays in the tree every day in summer. One day the ant is carrying some candy to her home. Her home is next to a big tree. The monkey is playing games in the tree. He says to the ant, “Why are you working every day? It is warm today. Don't work. Come and play games with me.” But the ant says, “Winter will come and it will be very cold. I want to store lots of food. I will sleep all day in winter.”
    Winter will not come soon. You can work in autumn,” says the monkey.
    Summer and autumn are over. There is snow(雪) everywhere. The monkey can't find any food. Do you know what will happen?

化学家门捷列夫说：“平静的水面练不出精悍的水手，安逸的环境造不出时代的伟人。”下列表述中符合这句话意思的是（    ）