B The Ancient Olympic Games古代奥林匹克运动会
According to historical records，the first (1) Olympic Games can be traced back to 776 BC.They (2) dedicated to the Olympian gods and were staged on the (3) plains of Olympia.They continued for nearly 12 centuries， (4) Emperor Theodosius decreed in 393 A.D.that aU such"pagan cults" (5) banned.
The oldest myth which concerns the beginning of the (6) Games is that of Idaios Daktylos Herakles.According to other (7) ，Zeus，the father of humanity，fought and defeated Cronus in a (8) for the throne of the gods.Finally，the well-known (9) Herakles is mentioned who staged games in Olympia in honour (10) Zeus,because the latter had helped him conquer Elis when (11) went to war against Augeas.
Through the 12 centuries of (12) Olympic Games，many wonderful athletes competed in the stadium and (13) hippodrome of ancient Olympia’s sacred area，moving the crowds with (14) great achievements.Although mortal，their Olympic victories immortalised them.Of (15) best athletes who left their mark on the sacred vallev (16) Olympia，some surpassed all limits and became legends by winning (17) successive Olympic Games and remaining at the forefront of their (18) for more than a decade.
The ancient Olympic Games were (19) a one.day event until 684 BC.when they were extended (20) three days.In the 5th century B.C.，the Games were extended again to cover five days.

下图表示人体内某些淋巴细胞的分化和免疫过程，数字表示过程，字母表示细胞或物质。请分析并回答：

造血干细胞在胸腺和骨髓内转变为a、b、c等细胞的过程被称为（），d为（）细胞.