**Core Concept**
Aspiration pneumonitis in infants often involves the lung segments that are most prone to aspiration and have a higher concentration of mucus glands. The right middle lobe (RML) and right lower lobe (RLL) are common sites of involvement in adults, but in infants, the upper lobes are more susceptible due to their anatomical position and the effects of gravity.

**Why the Correct Answer is Right**
The upper lobes are more likely to be involved in aspiration pneumonitis in infants due to their anatomical position, which makes them more susceptible to aspiration. The right upper lobe (RUL) is particularly prone to involvement because of its location and the presence of the azygos vein, which can divert aspirated material into the right lung. The mechanisms of aspiration and the anatomy of the infant's airways contribute to the higher incidence of RUL involvement.

**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable, as the question does not provide an option for this choice.
**Option B:** The left upper lobe is less commonly involved in aspiration pneumonitis in infants, as the left main bronchus is more vertical and less prone to aspiration.
**Option C:** The right lower lobe is more commonly involved in aspiration pneumonitis in adults, but in infants, the upper lobes are more susceptible.

**Clinical Pearl / High-Yield Fact**
In infants, the right upper lobe is the most common site of involvement in aspiration pneumonitis due to its anatomical position and the effects of gravity. This is a critical fact to remember when evaluating infants with respiratory symptoms.

**Correct Answer: C. Right middle lobe is not the most common, so the option that follows in the sequence that makes sense is the right lower lobe.