..... keeps the embryo attached to the wall of the uterus.

Options

A. The vagina
B. The blastula
C. The fallopian tube
D. The umbilical cord

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which structure is responsible for keeping the embryo attached to the wall of the uterus.

2. **Identifying Key Structures**: In human reproduction, the key structures involved in the attachment of the embryo to the uterine wall are the placenta and the chorion.

3. **Role of the Placenta**: The placenta is a crucial organ that forms during pregnancy. It serves multiple functions, including providing nutrients and oxygen to the developing embryo and removing waste products.

4. **Attachment Mechanism**: The placenta is formed from the chorion, which is a part of the embryo. The chorion develops finger-like projections called chorionic villi that penetrate the uterine wall, allowing for the attachment of the placenta.

5. **Conclusion**: Therefore, the structure that keeps the embryo attached to the wall of the uterus is the **placenta**.

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