**Core Concept**
The anatomical closure of the ductus arteriosus is a vital process in the transition from fetal to postnatal life. It involves the transformation of a patent arterial connection between the pulmonary artery and the aorta into a ligamentous structure, ensuring that oxygenated blood from the lungs is not shunted back to the aorta.

**Why the Correct Answer is Right**
The anatomical closure of the ductus arteriosus occurs due to the changes in oxygen tension and the subsequent increase in prostaglandin F2α degradation. As the ductus arteriosus is exposed to higher oxygen levels in the postnatal environment, the production of vasodilatory prostaglandins decreases, and the levels of vasoconstrictive prostaglandins increase. This shift in balance leads to the contraction of the ductus arteriosus, which eventually becomes fibrotic and transforms into the ligamentum arteriosum.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify a time frame or a mechanism for ductus arteriosus closure.
* **Option B:** This option is incorrect as it is not a recognized time frame or landmark for anatomical closure of the ductus arteriosus.
* **Option D:** This option is incorrect as it does not accurately describe the process of anatomical closure.

**Clinical Pearl / High-Yield Fact**
The anatomical closure of the ductus arteriosus typically occurs within 2-3 weeks after birth, but it can be delayed in conditions such as respiratory distress syndrome or cyanotic heart disease.

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