题目

The old couple chose to live _____ life was cheap, and they moved toa small town years ago.    A.  whose  B.  unless  C.  when  D.  where   答案：D下列人体细胞中分化程度最低的是A．胚胎干细胞B．造血干细胞C．胰腺细胞D．肌肉细胞