正确答案: B

+5

题目：五氧化二碘（化学式为I2O5）常用来测定空气中一氧化碳的含量，I2O5中碘元素化合价为

解析：B

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举一反三的答案和解析：

[单选题]25_______．

possible

[单选题]Which is true according to (根据)the passage?

The “Olympic Mathematics” is too difficult for kids.

[单选题]AMy name is Philip．Now I live in Beijing．On Sundays my father often takes me to movies． My favourite movies are action movies． My father likes them， too． Many young people like this kind of movies， because they are exciting． My good friend， Jim likes thrillers best． I don-t like thrillers． I think they are scary and boring． Jim likes Beijing Opera， too． And he wants to be a Beijing Opera artist．

Sundays

解析：21．A【解析】第三句可说明这一点。