胎盘合成雌三醇的前体物质主要来自()
A.合体滋养细胞
B.羊膜、叶状绒毛膜
C.胎儿肾上腺及胎儿肝脏
D.胎膜
E.脐带血
参考答案:C
While you are enjoying yourself in Beijing this time tomorrow, I __my mother do housework at home.
A.am helping
B.will help
C.would help
D.will be helping
当横波入射到平面缺陷时,在一定条件下,就会产生(),这种现象与横波()有关