第7题: [单项选择]在分布式数据库系统中,查询代价是由下列哪几项来衡量的______ ①CPU代价 ②I/O代价 ③通信代价 ④存储代价 A. ①②④ B. ①②③ C. ②③④ D. ①②③④ 参考答案:B 答案解析:[解析] 在分布式数据库系统中,查询代价不仅要考虑CPU代价和I/O代价,还要考虑站点间传输数据的通信代价。
A. had lost B. would have lost C. would lose D. should have lost 参考答案:B 答案解析:本题测试虚拟语气:条件从句使用过去完成时,主句一般使用would have done。例如:I would have been glad if she hadn’t come this morning