第23题: [单项选择]如果进栈序列为e1，e2，e3，e4，则可能的出栈序列是 A. e3，e1，e4，e2 B. e2，e4，e3，e1 C. e3，e4，e1，e2 D. 任意顺序 参考答案:B 答案解析:[解析] 由栈“后进先出”的特点可知：A) 中el不可能比e2先出；C) 中e1不可能比e2先出；D) 中栈是先进后出的，所以不可能是任意顺序。B) 中出栈过程如图所示： [*]
A. Mr. Black had never been to China before B. Mr. Black was an able and hardworking man C. Mr. Black could buy something interesting for Tony 参考答案:B 答案解析:[解析]由本文第一段第一行“Mr．Black was young and able．He worked very hard． And the boss liked him．”可知本题答案为B。
参考答案:It is reported that the local health organization was established 25 years ago/The local health organization is reported to have been established 25 years ago 答案解析:[解析] 本题考查形式主语it及被动语态的用法。It is reported that…意为“据报道…”，“为形式主语，后面的 that从句为句子的真正主语，表示“卫生组织成立”应该用被动语态。另外，
