从八边形的一个顶点可以引____ 条对角线．

为探究验证成分在空气中和人体呼出气体中含量的不同设计如下实验，（②③为人呼出气）

    Ms. Brown is a teacher. Her students are ____ these days because of (因为) the school ____ to the Summer Palace. It's next week. But she is so ____ these days and she doesn't have ____ to go. She tells her students about it and they are not happy. But at last, the students persuade (说服) her and she decides (决定) to go ____ with her dear students.