**Core Concept**
Placenta previa is a condition where the placenta partially or completely covers the internal cervical os, potentially leading to bleeding and other complications during pregnancy.

**Why the Correct Answer is Right**
In placenta previa, the placenta implants over the cervix, which can cause bleeding due to the separation of the placenta from the uterus. This is often diagnosed on ultrasound, where the placenta is seen covering part or all of the internal cervical os. The placenta previa can be classified into four types, including marginal (Type 1), low-lying (Type 2), partial (Type 3), and complete (Type 4).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a recognized classification of placenta previa.
**Option B:** This option might be a distractor for a different obstetric condition, but it does not describe a type of placenta previa.
**Option C:** This option might be a distractor for a different placental abnormality, but it does not describe a type of placenta previa.

**Clinical Pearl / High-Yield Fact**
It is essential for clinicians to recognize the different types of placenta previa, as this can affect management and treatment strategies. The American College of Obstetricians and Gynecologists (ACOG) recommends a detailed ultrasound evaluation to classify the type of placenta previa.

**Correct Answer:** D.