搜题请搜索小程序“爱下问搜题”
问题 单项选择题

关系R和S，RNS的运算等价于( )。

A．S-(R-S)

B．R-(R-S)

C．(R-S)∪S

D．R∪(R-S)

答案

参考答案：B

解析：[分析] 设关系R和关系S具有相同的目n，且相应的属性取自同一个域，由关系R与关系S的交属于R又属于S的元组组成，显然R∩S的运算等价于R-(R-S)。

完形填空

改写后的课文内容填空（共10个空，每空1分，满分10分）

Many people believe that “It is always calm before a storm.” Actually it is not true. Before the Tangshan earthquake, strange things happened. Some animals were too n______小题1: to eat and the water pipes in some buildings cracked and b______小题2:. At 3:42 a.m. the terrible earthquake broke out. In fifteen seconds, a large city lay in r_____小题3:. The suffering of the people was e_______小题4:. Almost everything was d_____小题5: and thousands of children were left homeless. Before people could r_______小题6:from the first quake, a second one hit the city. Some rescue workers and doctors were t________小题7:underground. Water, food, and e_______小题8:were cut off. People began to wonder how long the d____小题9: would last.

L_____小题10:， people all over the nation offered the helping hand. With the joint efforts, the city began to breathe again.
查看答案
问答题

简述银行办理打包贷款利息计算公式。如信用证的受益人于2008年11月9日要求 打包贷款。信用证的最迟装运日为12月31日，请计算出打包的天数，并说明原因。
查看答案