**Core Concept**
Iron absorption is a complex process regulated by various factors, including dietary iron content, pH in the stomach, and the presence of certain substances that enhance or inhibit absorption. In the duodenum, iron is absorbed through a process involving the reduction of ferric iron to ferrous iron, facilitated by the enzyme duodenal cytochrome b561, which is then transported into enterocytes through the divalent metal transporter 1 (DMT1).

**Why the Correct Answer is Right**
Vitamin C is a well-known enhancer of iron absorption, particularly non-heme iron. When consumed in conjunction with iron-rich foods, vitamin C increases the bioavailability of iron by reducing ferric iron to ferrous iron, which is more easily absorbed by the body. This occurs through a reduction-oxidation reaction where vitamin C donates electrons to ferric iron, converting it into ferrous iron.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ascorbic acid, or vitamin C, is a known enhancer of iron absorption and is not the correct answer.
* **Option B:** Citric acid, found in citrus fruits, also enhances iron absorption by chelating ferric iron and facilitating its reduction to ferrous iron.
* **Option C:** Meat consumption increases iron absorption by providing heme iron, which is more easily absorbed than non-heme iron found in plant-based foods.

**Clinical Pearl / High-Yield Fact**
It's essential to note that tea consumption, particularly black tea, can inhibit iron absorption due to its high polyphenol content, which can bind to iron and reduce its bioavailability.

**Correct Answer: D.**