第19题: [单项选择]People should be able to come to a decision about ions in the air if they ______. A. note their own reactions B. move to a healthier area C. observe domestic animals D. watch how wealthy people behave 参考答案:A 答案解析:[解析] 文章倒数第二句提到,人们可以通过观察环境对白己或他人的影响来判断负离子的富含或缺乏,所以选[A]。第二段末提到人们观察动物是为了预报灾难,而不是用来决定负离子数量是否合适,故排除 [C]。[