**Core Concept**
Umbilical cord anatomy is crucial in fetal development and delivery. The umbilical cord is a vital part of the placental circulation, responsible for transporting oxygenated blood and nutrients from the mother to the fetus and deoxygenated blood and waste products from the fetus to the mother.

**Why the Correct Answer is Right**
The correct anatomy of the umbilical cord is characterized by a single vein, known as the **vagina umbilicalis**, which carries deoxygenated blood and waste products from the fetus to the placenta. In contrast, there are two arteries, the **arteria umbilicalis dextra** and **arteria umbilicalis sinistra**, which carry oxygenated blood from the placenta to the fetus. This arrangement allows for efficient exchange of gases and nutrients between the mother and the fetus.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because there is only one vein in the umbilical cord, not two. The presence of two veins would disrupt the normal flow of blood and create a risk of thrombosis or other complications.
**Option C:** This option is incorrect because there are two arteries in the umbilical cord, not one. The presence of only one artery would limit the amount of oxygenated blood available to the fetus, potentially leading to growth restriction or other developmental problems.
**Option D:** This option is incorrect because there is only one vein in the umbilical cord, not two. The presence of two veins would create a risk of thrombosis or other complications, and would disrupt the normal flow of blood.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the umbilical cord typically measures between 50-60 cm in length and has a diameter of about 1-2 cm. Abnormalities in umbilical cord length or diameter can be a sign of underlying fetal or placental pathology.

**✓ Correct Answer: A. 1 vein and 2 arteries**