**Core Concept**
The question tests the understanding of types of twin pregnancies, which is an essential aspect of obstetrics and gynecology. A twin pregnancy occurs when two embryos develop in the uterus simultaneously, and it can be classified into different types based on the zygosity of the twins and their shared placenta.

**Why the Correct Answer is Right**
The most common type of twin pregnancy is dizygotic (fraternal) twins, which occur when two separate eggs are fertilized by two different sperm. This type of twin pregnancy accounts for about 70% of all twin births. The development of dizygotic twins is influenced by genetic factors, as well as environmental factors such as family history and fertility treatments. The placenta and amniotic sac of dizygotic twins are separate, which is a key distinguishing feature from monozygotic twins.

**Why Each Wrong Option is Incorrect**
**Option A:** Monochorionic diamniotic (MoDi) twins are a type of monozygotic twins, where two separate amniotic sacs are present, but they share a single placenta. This is not the most common type of twin pregnancy.
**Option B:** Diamniotic dichorionic (DiDi) twins are a type of dizygotic twins, where two separate placentas and amniotic sacs are present. While this is a common type of twin pregnancy, it is not the most common.
**Option C:** Monochorionic monoamniotic (MoMo) twins are a type of monozygotic twins, where a single amniotic sac is present, and they share a single placenta. This is a rare type of twin pregnancy.

**Clinical Pearl / High-Yield Fact**
It is essential to know the type of twin pregnancy to plan the delivery and manage potential complications. Dizygotic twins are more common and generally have a better prognosis than monozygotic twins.

**Correct Answer: D. Dizygotic twins are the most common type of twin pregnancy, accounting for about 70% of all twin births.**