某百米短跑运动员，他的成绩为10秒，如果他在前5秒内的平均速度为9m/s；冲过终点的时速度达到13m/s，那么他跑完全程的平均速度为（　　）

阅读下面的诗歌。
                                                                                              滁州西涧
                                                                                                韦应物
                                                                                        独怜幽草涧边生，
                                                                                       上有黄鹂深树鸣。
                                                                                       春潮带雨晚来急，
                                                                                        野渡无人舟自横。