**Core Concept**
The placental barrier is crucial for separating fetal blood from the maternal bloodstream, and it consists of several layers, including the syncytiotrophoblast. This barrier is essential for preventing the direct contact of fetal blood with maternal immune cells.

**Why the Correct Answer is Right**
Since the question is incomplete, let's discuss the general structure of the placental barrier. The fetal blood is separated from the syncytiotrophoblast by the cytotrophoblast layer and the basal lamina in some areas, but the main structure that separates fetal blood from the syncytiotrophoblast is the fetal capillary endothelium.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific details of option A, we cannot provide a detailed explanation.
**Option B:** Similarly, without the details of option B, we cannot explain why it is incorrect.
**Option C:** The same applies to option C.
**Option D:** And option D.

**Clinical Pearl / High-Yield Fact**
The placental barrier is crucial for preventing the exchange of immune cells between the mother and the fetus, thus preventing an immune response against the fetus.

**Correct Answer:** Correct Answer: D. Basal lamina is not the structure that directly separates fetal blood from syncytiotrophoblast in all areas, but without the question details, this is speculative.