问题 单项选择题

下列关于E-R图的描述中正确的是

A.E-R图只能表示实体之间的联系

B.E-R图只能表示实体和实体之间的联系

C.E-R图只能表示实体和属性

D.E-R图能表示实体、属性和实体之间的联系

答案

参考答案:D

解析: E-R(实体—联系,Entity-Relationship)图是设计概念模型的有力工具。在E-R图中,用三种图框分别表示实体,属性和实体之间的联系: ①用矩形框表示实体,框内标明实体名; ②用椭圆状框表示实体的属性,框内标明属性名; ③用菱形框表示实体问的联系,框内标明联系名; ④实体与其属性之间以无向边连接,菱形框与相关实体之间也用无向边连接,并在无向边旁标明联系的类型。 因此,用E-R图不仅可以简单明了地描述实体及其相互之间的联系,还可以方便地描述多个实体集之间的联系和一个实体集内部实体之间的联系。 由此可知,选项A、B、C二个选项中的既法都是不对的。

完形填空

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项

To Build a Bridge

The Brooklyn Bridge that spans the river tying Manhattan Island to Brooklyn is truly a miracle(奇迹) bridge. 小题1:____ However, bridge­building experts throughout the world told him to forget it; it could not be done.

Roebling convinced his son, Washington, who was a young up-and-coming engineer, that the bridge could be built. 小题2:_______ With excitement and inspiration, they hired their crew and began to build their dream bridge.

The project was only a few months under construction when a tragic accident on the site took the life of John Roebling and severely injured his son, Washington. 小题3:_____ Everyone felt that the project would have to be stopped since the Roeblings were the only ones who knew how the bridge could be built.

小题4:_______ And he still had a burning desire to complete the bridge. An idea hit him as he lay in his hospital bed, and he developed a code for communication.小题5:___ So he touched the arm of his wife with that finger, tapping out the code to communicate to her what to tell the engineers who were building the bridge. For thirteen years, Washington tapped out his instructions with his finger until the spectacular Brooklyn Bridge was finally completed.

A.Even though Washington was unable to move or talk, his mind was as sharp as ever.

B.In 1863, a creative engineer named John Roebling was inspired by an idea for this spectacular bridge.

C.A promising engineer was hired to build the difficult bridge which is unbelievable.

D.The two of them developed the concepts of how it could be accomplished and how the obstacles could be overcome.E.Hard as it is, Roebling got through all difficulties to complete the bridge.

F.Washington was left with permanent brain damage and was unable to talk or walk.

G.All he could move was one finger.

单项选择题 配伍题