第2题: [单项选择]设有栈S和队列Q，其初始状态为空，元素a1、a2、a3、a4、a5、a6依次入栈，出栈的元素则进入队列Q，若6个元素出列的顺序是a2、a4、a3、a6、a5、a1，则栈的容量至少要有几个单元 A. 6 B. 4 C. 3 D. 2 参考答案:C 答案解析:[解析] 考虑到一个元素在入栈之前，另一个元素可能出栈的情况，再根据出栈情况来判断，栈中至少要有3个单元存放最后出栈的a6、a5、a4 3个元素。
第31题: [单项选择]{{B}}Passage One{{/B}} A. To keep selling them to people by producing cigarettes with less tar. B. To persuade people to give up smoking entirely. C. To reduce the risk to people’s health. D. To let people know the risk to people’s health. 参考答案:B 答案解析:[听力原文]
What are health experts trying to do
