**Core Concept**
The placental barrier is crucial for separating fetal blood from the maternal bloodstream, and it consists of several layers, including the syncytiotrophoblast. The **syncytiotrophoblast** is the outermost layer of the trophoblasts, which invades the uterine lining during implantation.

**Why the Correct Answer is Right**
Since the question is incomplete, let's discuss the general structure. Normally, fetal blood is separated from the **syncytiotrophoblast** by the cytotrophoblast layer and the basement membrane in some areas, but directly in contact in others, specifically at the **chorionic villi** tips where exchange occurs.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific details of option A, it's challenging to provide a precise explanation.
**Option B:** Similarly, without the details, we can't determine why it might be incorrect.
**Option C:** And option C, lacking specifics, can't be directly addressed.
**Option D:** The same issue applies to option D.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **placental barrier** allows for the exchange of gases, nutrients, and waste between the maternal and fetal blood without direct contact between the two blood supplies, which is crucial for fetal development and maternal health.

**Correct Answer:** Correct Answer: D. Basal lamina