**Core Concept**
The placenta is a vital organ that develops in the uterus during pregnancy, playing a crucial role in providing oxygen and nutrients to the fetus and removing waste products. It is formed from both maternal and fetal tissues. The development of the placenta involves the **trophoblast** cells of the embryo and the **endometrium** of the mother.

**Why the Correct Answer is Right**
The correct answer involves the understanding that the placenta is formed from two main sources: the fetal part, which is derived from the **chorion frondosum**, and the maternal part, which is derived from the **endometrium**. The **trophoblast** cells invade the endometrium, leading to the formation of the placenta.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the dual origin of the placenta.
**Option B:** This option is also incorrect as it only mentions one component.
**Option C:** Similarly, this option is incorrect as it does not fully describe the development of the placenta.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the placenta is a fetomaternal organ, and its development is crucial for the survival of the fetus. Any abnormalities in placental development can lead to complications in pregnancy.

**Correct Answer:** D. Both maternal and fetal tissues.