<prompt> Placenta develops from:Chorion frondosum and decidua basalisChorion villi and decidua basalisChorion frondosum and decidua capsularisChorion villi and decidua parietalis  <response>: Ans. A. Chorion frondosum and decidua basalis1. The human placenta is of chorioallantoic type, consisting of 2 components:a. The chorion, or outer layers of the chorionic cavity, including:i. The syncytiotrophoblastii. The cytotrophoblastiii. The extraembryonic mesodermb. The allantois, containing the umbilical vessels and 3 foetal blood vessels: 2 arteries and 1 vein.2. The foetal trophoblast invades the endometrium, breaks down the endometrial blood vessels into lacunae, and forms villi around them.3. Thus, the placenta is a materno-foetal unit, with:i. The foetal portion formed by the chorion chorionic plateii. The maternal portion formed by the decidua basalis basal plate.4. The foeto-maternal interface consists of these opposed layers:i. The chorion frondosumii. Fibriniii. The decidua basalis 