During implantation, the trophoblast divides into two layers. The innermost layer, the _________, becomes the chorionic villi, and an outermost layer, the ___________, which forms the decidua basalis and main placental tissue.

During implantation, the trophoblast divides into two layers. The innermost layer, the _________, becomes the chorionic villi, and an outermost layer, the ___________, which forms the decidua basalis and main placental tissue. 



A. chorion; amnion
B. chorion; embryoblast
C. syncytiotrophoblast; cytotrophoblast
D. cytotrophoblast; syncytiotrophoblast
E. embryoblast; amnion


Answer: D. cytotrophoblast; syncytiotrophoblast


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