**Core Concept**
Monozygotic twins, also known as identical twins, are formed when a single fertilized egg (zygote) splits and develops into two separate embryos. This results in two individuals with nearly identical DNA, which is the primary reason for their identical physical appearance.

**Why the Correct Answer is Right**
However, despite their identical genetic makeup, monozygotic twins do not have the same placenta or chorionic villi. This is because the split usually occurs after 3-4 days of development, when the embryo has already implanted in the uterus. As a result, each twin develops its own placenta and chorionic villi, which can lead to differences in the development of certain organs, such as the brain, heart, and pancreas. These differences can also lead to variations in the twin's immune system, which may affect their susceptibility to certain diseases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because monozygotic twins, by definition, have the same DNA.
**Option B:** This option is incorrect because monozygotic twins typically have similar blood types, which are determined by genetics.
**Option C:** This option is incorrect because monozygotic twins usually have similar fingerprints, which are formed by genetic factors.

**Clinical Pearl / High-Yield Fact**
It's worth noting that monozygotic twins can still have differences in their development, which can be influenced by various factors, such as the timing of the split and the environment in which they develop. This highlights the importance of considering the unique characteristics of each individual, even in identical twins.

**Correct Answer:** D. Placenta