[单项选择]出现单个流行高峰后，接着出现一批病例，在流行曲线上形成一个尾巴、这往往是由于（）
A. 共同媒介传播后继之以接触传播
B. 接触传播后继之似共同传播
C. 通过接触疫水传播
D. 通过接触生物媒介传播
E. 生物媒介传播和接触疫水传播同时存在

C 　　When I was looking for a Christmas present for my daughter in a toy store, a nicely dressed little girl, with some money in her little hand, was looking at some beautiful dolls. When she saw a doll she liked, she would ask her father if she had enough money. He usually said yes. 　　At the same time, a boy, with old and small clothes, was looking at some video games. He, too, had money in his hand, but it looked no more than five dollars. Each time he picked up one of the video games and looked at his father, he shook his head. 　　The little girl had chosen her doll, a very beautiful one. However, she noticed the boy and his father. She saw the boy give up a video game with disappointment(失望) and walk to another corner of the store. 　　The little girl put her doll back to the shelf and ran over to the video game. After she talked to her father, she paid for the video game and whispered(耳语) to the shop assistant. 　　So the boy got the video game that he wanted for free—he was
A. The little girl was kind and helpful.
B. The video game was a prize from the store.
C. The writer paid for the video game for the boy.
D. The boy bought the video game himself from the store.