单项选择题
A.卵黄囊 B.中胚叶 C.肝脏 D.骨髓 E.脾脏
A.90g/L B.100g/L C.110g/L D.120g/L E.130g/L
A.4岁 B.6岁 C.8岁 D.10岁 E.12岁