山东省普通高等教育专升本模拟考试
第二部分:用法和语法结构(Part II Vocabulary and Structure), 共30题,考试时间为20分钟。从题中所给的A, B, C,D四个选项中选出最佳答案。
21 I'm sorry ______ answered your letter earlier.
A. having not B. not having C. not to have D. to not have
22. _____ had they got into the classroom _____ the bell rang.