白血病是一种常见的造血组织肿瘤性疾病。该病是由于造血干细胞中原癌基因发生突变，使之变成不受机体控制、连续进行分裂的恶性增殖细胞。而在正常的情况下，人体血液中的红细胞、白细胞、血小板都是通过造血干细胞形成的。正常的造血干细胞通过下列哪些过程完成对血细胞的补充（   ）
①细胞增殖 ②细胞分化 ③细胞凋亡

1mol H₂表示的含义是（　　）

   A leading biologist has found the angels and fairies that sit at top of Christmas trees did not get there under their own power.
   Prof Roger Wotton, from University College London, found that flight would be impossible for angels with arms and bird-like feathered wings. 
   "Angels cannot take off and cannot use powered flight,” said Prof Wotton. “They would need to be exposed to very high wind velocities at take off - such high winds that they would be blown away."
   Some the world’s most famous religious paintings and architecture make most Americans believe in angels.
   The study found that 68 per cent of the 36,000 adults thought that angels and demons (魔鬼) were at work in the world.
   According to the latest study, angels lack the powerful muscles which allow birds to beat their wings. Prof Wotton's paper explores why there are so many stories about angels. “Angels are very powerful religious icons for people with faith. Their similarity to humans adds to their power. At the same time, they have wings on them because they are more than human. They take messages to heaven and therefore have to fly.” said the academic.