下面关于串行通信的叙述中，错误的是()。
A．异步通信时，起始位和停止位用来完成每一帧信息的收发同步
B．二进制数据序列在串行传送过程中，无论是发送还是接收，都必须由时钟信号对传送数据进行定位
C．串行通信有单工、半双工和全双工三种方式
D．对传送数据进行校验时，如果发送方按偶校验产生校验位，那么接受方可按偶校验进行校验，也可按奇校验进行校验
参考答案：D
解析：在原型化方法的需求定义阶段，需求定义应具有以下属性：完备性：所有需求都必须加以说明。一致性：需求之间没有逻辑上的矛盾。非冗余性：不应该有多余的、含糊不清的需求说明。可理解性：参加各方应以一种共同的方式来解释和理解需求。可测试性：需求必须能够验证。可维护性：文档的组织必须是可灵活修改和易读的。正确性：所规定的需求必须是用户所需求的。必要性：需求应是准确的和完整的。
| 完形填空。 | |||
| I have a good friend. His name is Sonny. He l Sydney , Australia. Now he lives in Beijing with his parents. He's 14 2 and his birthday is 3 October. He speaks English and he 4 speaks 5 Chinese. He has lots of friends in Beijing. He often 6 after school with them. It's his favorite sport. On weekends, he likes 7 to the movies with his friends. He likes Chinese action movies very much. He thinks they're very exciting. His favorite actor is Jackie Chan. And his favorite 8 in the school are computer and math. They're fun. But he 9 history. He thinks it is boring. He is very clever and lovely. All my teachers and classmates like him. Do you 10 make friends with him? | |||
| ( )1. A. come from ( )2. A. years ( )3. A. in ( )4. A. too ( )5. A. a few ( )6. A. watches TV ( )7. A. goes ( )8. A. sports ( )9. A. likes ( )10. A. want | B. from B. years old B. on B. either B. few B. goes shopping B. going B. subject B. don't like B. wants | C. are from C. ages C. at C. also C. a lots of C. plays soccer C. go C. movies C. doesn't like C. wants to | D. comes from D. year old D. / D. want D. a little D. goes to the movies D. to going D. subjects D. like D. want to |