A. occasionally B. simultaneously C. eventually D. promptly 参考答案:B 答案解析:[解析] 副词辨义。这四个选项都是副词,occasionally表示“偶然,偶尔;有时”,如:We go for walks in the fields occasionally.(我们有时会到田野散
第28题: [单项选择]关系R1、R2的结构相同,各有10个元组,那么这两个关系的并操作结果的元组个数 A. 10 B. 小于等于10 C. 20 D. 小于等于20 参考答案:D 答案解析:[解析] 并是关系代数基本运算之一。设R和S具有相同的关系模式(同类关系) ,则R和S的并是由属于R或属于S或同时属于R和S的元组组成的集合。从定义中不难看出,两个关系的并所包含的元组个数应满足:MA
第32题: [单项选择]Why does the professor prefer these particular days for the tutorial A. The students prefer these days the most. B. The course runs from Monday to Wednesday. C. He likes to control every detail of the course. D. He is out of town these particular days each week. 参考答案:B 答案解析:[解析] 推理题 教授在对话中说想给学生们复习的时间(…because I want my students to have some time to review things covered du