The chorion that forms during the second week of development consists of the ___ the ___ and the ___
a. syncytiotrophoblast; cytotrophoblast; maternal sinusoids
b. maternal sinusoids; extraembryonic mesoderm; cytotrophoblast
c. extraembryonic mesoderm; syncytiotrophoblast; maternal sinusoids
d. extraembryonic mesoderm; syncytiotrophoblast; cytotrophoblast