## Core Concept
Restrictive lung disease is characterized by a decrease in lung volume, resulting in reduced total lung capacity (TLC). This category of lung disease includes conditions such as pulmonary fibrosis, sarcoidosis, and neuromuscular disorders that affect lung expansion.

## Why the Correct Answer is Right
In restrictive lung disease, the lung volumes are decreased, which leads to a reduction in the total lung capacity (TLC). The forced vital capacity (FVC) is also decreased, but the ratio of forced expiratory volume in one second (FEV1) to FVC is normal or even increased because both FEV1 and FVC are reduced proportionally. This results in a normal or increased FEV1/FVC ratio, distinguishing it from obstructive lung diseases where this ratio is decreased.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, in restrictive lung disease, the TLC is decreased, not increased.
- **Option B:** This option is incorrect because, although FVC is decreased in restrictive lung disease, stating it as "increased" is incorrect.
- **Option C:** This option might seem plausible but is incorrect because, in restrictive lung disease, FEV1/FVC ratio is normal or increased, not decreased.

## Clinical Pearl / High-Yield Fact
A key clinical pearl for restrictive lung disease is that patients often present with shortness of breath and have a reduced lung volume on pulmonary function tests, which helps differentiate it from obstructive lung diseases like COPD.

## Correct Answer: D.