Today is Friday. Peter has six classes today. He goes to school at 7:30 a.m. At 8:00 a.m., he begins his first class. The first class is English. At 9:00 a.m., he has math. Peter likes math because it’s interesting. At 10:00 a.m. she has a biology class. Peter thinks it's very boring. Then at 11:00 a.m., he has a history class. That's his favorite subject. He can learn a lot about the past from history.
    Peter has lunch at school at about 12:00. Then he has a short break. At 1:30 p.m., he has a music class. At 2:30 p.m., he has a P.E. class. Peter likes this afternoon, because music and P.E. are easy and interesting. School is over at 4:00 p.m. Peter is happy because he can go home and have a good time on Saturday and Sunday.
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某溶液中只含有Na⁺、Al³⁺、Cl^－、SO₄^2－四种主要离子(其余离子可忽略)，已知前三种离子的个数比为3∶2∶1，则溶液中Al³⁺和 SO₄^2－的离子个数比为

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抗日战争时期，***在根据地实行地主减租减息、农民交租交息的土地政策。这一政策的特点是(　　)