The characteristic features of placental mammals are

Options

A. Absence of marsupium or epipubic bone
B. Presence of a ture placenta
C. Viviparous
D. All of the above

Answer

### Step-by-Step Solution:

1. **Definition of Placental Mammals**:
- Placental mammals, also known as eutherians, are a group of mammals characterized by the presence of a well-developed placenta. This organ plays a crucial role in the development of the embryo during gestation.

**Hint**: Remember that the term "placental" directly refers to the presence of the placenta in these mammals.

2. **Function of the Placenta**:
- The placenta serves two primary functions: it provides nutrients from the mother to the developing fetus and removes waste products from the fetus back to the mother. This connection allows for a more efficient exchange of substances necessary for fetal development.

**Hint**: Think of the placenta as a lifeline between the mother and the developing young.

3. **Absence of Marsupium and Epipubic Bone**:
- Unlike marsupials (like kangaroos), placental mammals do not have a marsupium (a pouch) or an epipubic bone. These features are specific to certain groups of mammals and are not found in placental mammals.

**Hint**: Compare placental mammals with marsupials to understand the differences in reproductive structures.

4. **Presence of True Placenta**:
- The defining characteristic of placental mammals is the presence of a true placenta, which allows for the prolonged gestation of the young inside the mother's body.

**Hint**: Focus on the term "true placenta" to distinguish placental mammals from other types of mammals.

5. **Viviparous Nature**:
- Placental mammals are viviparous, meaning they give birth to live young rather than laying eggs (which is the case for oviparous animals). The development of the young occurs inside the mother, facilitated by the placenta.

**Hint**: Remember that "viviparous" relates to live birth, contrasting with "oviparous," which refers to egg-laying.

6. **Conclusion**:
- The main characteristic features of placental mammals include the presence of a true placenta, the absence of a marsupium and epipubic bone, and their viviparous reproductive strategy.

**Hint**: Summarize the characteristics by focusing on the role of the placenta and the reproductive differences from other mammalian groups.

### Summary of Characteristic Features of Placental Mammals:
- Well-developed placenta for nutrient and waste exchange.
- Absence of marsupium and epipubic bone.
- Viviparous reproduction (live birth).