问题 单项选择题

设关系R和S的元数分别是r和s,则它们的笛卡尔积是一个多少个元组的集合

A.r+s

B.r×s

C.r∩s

D.r∈s

答案

参考答案:A

解析: 本题考查的是两关系的笛卡尔积的定义。两个分别为N目和M目的关系R和S的广义笛卡尔积是一个(N+M)列的元组。若R有K1个元组,S有搬个元组,则关系R和S的广义笛卡尔积有 K1×K2个元组。

完形填空

完形填空。 (10分)

Mrs. Andrews had a young cat, and it was the cat’s first winter. One evening it was __1___ when it began to snow heavily. Mrs. Andrews looked __2___ everywhere and shouted its name, but she did not find it, __3___ she telephoned the police and said, “ I have ___4___ a small black cat. Has ____5____ found one?”

“No, madam,” said the policeman at the other end, “But cats are really very __6___ animals. They sometimes live for days in the snow, and when it melts(融化)and somebody finds them, they are quite ____7____.”

Mrs. Andrews felt ____8___ when she heard this “And”, she said, “Our cat is very ____9___. She almost talks.”

The policeman was getting rather tired. “Well then,” he said, “Why don’t you put your __10____ down? Maybe she is trying to telephone you now.”

(   )1. A. here        B. there       C. inside         D. outside

(   )2. A. at          B. for         C. after          D. around

(   )3. A. so          B. or          C. if            D. because

(   )4. A. got         B. sold        C. lost           D. bought

(    )5. A. he          B. she        C. anybody       D. everybody

(   )6. A. bad         B. good       C. weak          D. strong

(   )7. A. well         B. ill         C. careful       D. worried

(    )8. A. worse       B. happier     C. colder         D. younger

(    )9. A. busy        B. clean       C. clever         D. angry

(   )10.A. cat         B. book       C. hands         D. telephone

单项选择题 A1型题