第12题: [单项选择]数据模型的三要素是______。 A. 外模式、概念模式和内模式 B. 关系模型、网状模型、层次模型 C. 实体、属性和联系 D. 数据结构、数据操作和数据约束条件 参考答案:D 答案解析:[解析] 数据结构、数据操作和数据约束条件这三个方面完整地描述了一个数据模型，其中数据结构是刻画模型性质的最基本的方面。
第14题: [单项选择]There was a heated debate over the policies for preventive services of ______. A. stomach cancer B. breast cancer C. kidney cancer D. lung cancer 参考答案:B 答案解析:[听力原文] Sometimes new health advice conflicts with old advice. Yet new policies last week for
第18题: [单项选择]{{B}} Questions 11 to 18 are based on the conversation you have just heard.{{/B}} A. His computer doesn’t work well. B. He isn’t getting along with his staff. C. He didn’t register for a proper course. D. He can’t apply the theory to his program. 参考答案:D
