**Core Concept**
The **ductus arteriosus** is a fetal blood vessel that connects the pulmonary artery to the aortic arch, allowing blood to bypass the lungs. After birth, it undergoes anatomical closure. This process involves **smooth muscle contraction** and **endothelial thickening**.

**Why the Correct Answer is Right**
Anatomical closure of the ductus arteriosus occurs within the first few weeks of life, typically around 2-3 weeks. This is due to the increase in oxygen tension after birth, which stimulates the **prostaglandin** pathway to decrease, leading to **smooth muscle contraction** and eventual **fibrosis**.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it refers to a time frame that is too early for anatomical closure.
**Option B:** This option is also incorrect as it is not specific to the anatomical closure process.
**Option D:** This option is incorrect because functional closure occurs earlier than anatomical closure.

**Clinical Pearl / High-Yield Fact**
Remember that **prostaglandin E** plays a key role in keeping the ductus arteriosus open during fetal life. After birth, the decrease in prostaglandin levels allows for closure.

**Correct Answer:** C. 2-3 weeks