**Core Concept**
The underlying concept being tested is the anatomy of the placenta, specifically the types of placenta classified based on the insertion of the umbilical cord. This knowledge is crucial for understanding placental development and potential complications in pregnancy.

**Why the Correct Answer is Right**
A placenta with the umbilical cord attached to its margin is known as a **battledore placenta**. This type of placenta is characterized by the umbilical cord inserting at the very edge of the placental mass. The mechanism behind this classification is based on the normal variation in umbilical cord insertion points, which can be central, marginal (battledore), or velamentous.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not specify the marginal insertion of the umbilical cord.
**Option B:** Incorrect as it refers to a different condition.
**Option D:** Incorrect because it is not related to the marginal insertion of the umbilical cord.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that the type of placenta and umbilical cord insertion can have implications for fetal development and pregnancy outcomes. A battledore placenta is generally considered a normal variant but knowing its characteristics can help in identifying potential issues early.

**Correct Answer:** D. Battledore placenta.