搜题请搜索小程序“爱下问搜题”
问题 填空题

用值域的概念来定义关系，关系是属性值域笛卡尔积的一个______。

答案

参考答案：子集

解析：

[分析]： 用值域的概念来定义关系，关系就是属性值域进行笛卡尔积的一个子集。

填空题

I live in the country and my father was a farmer.51. ______
He is now forty-five year old. Because of years of 52. ______
hard work, he looks old than his age. When I was53. ______
young, he is used to tell me the importance of study. 54. ______
Father knows little about English and other subjects, 55. ______
but he usually gives me some good advices on how56. ______
to learn my lessons good. He is not only kind to me 57. ______
but also very strict in me. With his help, I’ve made 58. ______
great progress. I’ll never to forget what he taught 59. ______
me. I think my father is best father in the world. 60. ______
查看答案
填空题

化学沉积分异的大致次序是氧化物→硅酸盐→碳酸盐→（）。
查看答案