简述对象联系图的定义。
参考答案:对象联系图是描述面向对象数据模型的基本工具。它不仅完整地揭示了数据之间的联系,也把查询的层次观点表现得一清二楚。
阅读填词。根据短文内容和所给的首字母,写出文中各空缺单词的正确形式。
It was the first time for most of us to be abroad (国外). So when we g 1 on the plane, we were very
e 2 .It took about nine h 3 to fly to London, but we didn't feel how long b 4 the service (服务) on the
plane was very good. We saw three English films. On the w 5 to the college (大学), we found very f 6
people on the road but (除了) a lot of cars. We could see many buildings, green grass, forests and large
parking places. We lived in d 7 families and I lived in Mr Bank's. The Banks were very k 8 to me. They
have got a son n 9 Ben, and we soon became good f 10 .
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皮带胶接头的合拢,要求以()向()以利于将空气排气。