纵隔生殖细胞瘤从胚胎发育上来源于何处（）.
A.第3、4腮弓
B.胎儿尿生殖嵴
C.胸腺干细胞
D.迷走原始生殖细胞
E.卵黄囊
参考答案：E
The best way to make a kid to be independent is to put him in a position ________ he has no one
else to refer to.[ ]
A. that
B. what
C. where
D. which
乙烯自燃点为（）℃，分子式C2H在空气中的爆炸极限为3.05---28.6%
