Placenta is present in

Options

A. All mammals
B. Metatherians
C. Eutherians
D. Prototherians

Explanation

**Step-by-Step Solution:**

1. **Understanding the Placenta**: The placenta is an organ that develops in the uterus during pregnancy. It plays a crucial role in the exchange of nutrients, gases (like oxygen and carbon dioxide), and waste products between the mother and the developing fetus.

2. **Identifying Classes of Mammals**: Mammals can be classified into three main subclasses:
- **Prototherians**: These are egg-laying mammals (e.g., platypus and echidna).
- **Metatherians**: These are marsupials that give birth to underdeveloped young (e.g., kangaroos and koalas).
- **Eutherians**: These are placental mammals that give birth to fully developed young (e.g., humans, dogs, and elephants).

3. **Analyzing the Options**: The question asks about the presence of the placenta in these subclasses:
- **Option A: Prototherians** - They do not have a placenta as they lay eggs.
- **Option B: Metatherians** - They have a very rudimentary placenta, but it is not fully developed like that of eutherians.
- **Option C: Eutherians** - They possess a well-developed placenta that supports the fetus throughout its development in the uterus.

4. **Conclusion**: Based on the analysis, the correct answer is that the placenta is present in **Eutherians** (Option C).

**Final Answer**: The placenta is present in Eutherians.

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