![](https://static.youtibao.com/asksite/comm/h5/images/m_q_title.png)
[单选题]
关于两胚层embryonic disc 的描述,正确的是()
A.由胚泡滋养层细胞增殖形成
B.由外胚层和上胚层组成
C.由内胚层和下胚层组成
D.上胚层组成羊膜囊的底
E.下胚层构成羊膜囊的顶
![](https://static.youtibao.com/asksite/comm/h5/images/m_q_a.png)
D、上胚层组成羊膜囊的底
![](https://static.youtibao.com/asksite/comm/h5/images/solist_ts.png)
A.由胚泡滋养层细胞增殖形成
B.由外胚层和上胚层组成
C.由内胚层和下胚层组成
D.上胚层组成羊膜囊的底
E.下胚层构成羊膜囊的顶
D、上胚层组成羊膜囊的底
A trifled with B scraped through C stumbled upon D thirsted for
The question______at the next meeting remains a secret.
A.discussed
B.to discuss
C.to be discussed
D.being discussed