题目

Bill Gates was born on October 28, 1955. He grew up in Seattle, Washington. He was a very clever boy. His favorite subjects at school were science and math. When he was 13, he started to play with computers. At that time, computers were large machines. Once he was very interested in a very old computer. He and some of his friends spent lots of time doing unusual things with it. In the end, they worked out a software program with the old machine. Bill sold it for $4,200 when he was only 17. In 1973, Bill went to Harvard University(哈佛大学). In his third school year, he left Harvard t观察小鱼尾鲜血液流动时，血流速度最慢的血管是（　　）A．小动脉B．小静脉C．毛细血管D．小动脉和小静脉