**Core Concept**
The placenta is a vital organ that develops in the uterus during pregnancy, facilitating the exchange of nutrients, gases, and waste products between the mother and the fetus. The syncytiotrophoblast, a layer of multinucleated cells, plays a crucial role in this process by forming the fetal-maternal interface. The separation of fetal blood from the syncytiotrophoblast is essential to prevent direct contact between the two and maintain the integrity of the placental barrier.

**Why the Correct Answer is Right**
The correct answer is related to the structure of the placenta, specifically the layer that separates fetal blood from the syncytiotrophoblast. The trophoblast layer, which includes the cytotrophoblast and syncytiotrophoblast, is the outermost layer of the placenta. The cytotrophoblast is a single layer of cells that lies beneath the syncytiotrophoblast, while the fetal blood flows through the intervillous space, surrounded by the villi.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the cytotrophoblast lies beneath the syncytiotrophoblast and is not the layer that directly separates fetal blood from the syncytiotrophoblast.
**Option B:** This option is incorrect because the chorionic villi are the finger-like projections that increase the surface area for exchange between the mother and the fetus, but they are not the layer that separates fetal blood from the syncytiotrophoblast.
**Option C:** This option is incorrect because the basal plate is the layer of cytotrophoblast cells that lies beneath the chorionic plate and is not the layer that separates fetal blood from the syncytiotrophoblast.

**Clinical Pearl / High-Yield Fact**
The placenta is a dynamic organ that undergoes significant changes throughout pregnancy, and understanding its structure and function is crucial for managing complications such as placenta previa and placental abruption.

**Correct Answer:** D.