我国著名化学家徐辉碧教授根据众多实验事实，提出了硒元素（Se）与艾滋病的发生和发展有关．K₂SeO₄是一种含硒的化合物，其中硒元素的化合价为（    ）

如图程序的功能是（　　）

先通读下面的短文，掌握其大意，然后从A、B、C、D四个选项中选择可以填入空白处的最佳答案。

    Carol is a middle school student；She does well in only one subject.That is1.  Carol always does her history homework well and2good grade(分数)in history tests She likes her history teacher Mr．Aragon．She feels that he is like her3．

    At a parent—teacher meeting，Carol's mother has a4with Mr．Aragon．She says that Carol doesn't do well in5subjects．She hopes Mr．Aragon can6her．"Oh．I didn't know that．She is7．I'll try to talk to her,"says Mr．Aragon．

    When Mr．Aragon talks with Carol8her other subjects，Carol doesn't feel good，9she is grateful(感激的)．She knows that Mr．Aragon is trying to help．Carol 10his advice(建议)and tries to do well in other subjects．