读“我国东南沿海某区域附近地区地形图和河流剖面示意图”,回答下列各题

    Anna is a Chinese girl . She is ten . She is in London with her parents. She doesn't know much English. She can't speak English well. Sometimes her friends don't understand her .

    It's Sunday morning .She is going to the zoo to see the panda . She is waiting at a bus stop .At the bus stop she asks a boy how to go to the zoo. But the boy can't understand her .Then she takes out a pen and some paper. She draw a panda on it and shows the picture to the boy .The boy smiles and then shows her the way to the zoo.

在氢硫酸溶液中加入少量下列物质：①O₂；②Cl₂；③SO₂；④CuSO₄．能使溶液pH值减小的是（　　）