This human is lucky, because if you miss just two letters in this position -- two letters of our three billion -- he will be condemned to a terrible disease: cystic fibrosis.
这个人很幸运， 因为如果他在这个位点上少了2个字母， 30亿中的2个... 他就会患上一种非常可怕的疾病—— 囊肿性纤维化