胚胎中胚层造血首先形成血岛的是
A.骨髓
B.肝脏
C.脾脏
D.卵黄囊
E.胸腺
参考答案:D
A Tale of Two Cities is ______ a novel. It helps us to understand the history of that time.
A.not more than
B.no more than
C.less than
D.more than
水的硬度表示方法有多种,我国采用的方法与()国相同。