**Core Concept**
In restrictive pulmonary diseases, lung function is impaired due to a reduction in lung volume, making it difficult for the lungs to expand and fill with air. This results in decreased lung capacity and efficiency in gas exchange. The key concept here is the distinction between restrictive and obstructive lung diseases.

**Why the Correct Answer is Right**
In restrictive pulmonary diseases, the lung compliance (the ability of the lungs to expand) is decreased, but the airway resistance remains normal. Therefore, the lung volume measurements such as Total Lung Capacity (TLC) and Functional Residual Capacity (FRC) are decreased, but the airway resistance and lung volumes measured at the end of a maximal exhalation, such as Residual Volume (RV), are preserved. This makes the measurement of Residual Volume (RV) likely to be normal.

**Why Each Wrong Option is Incorrect**
**Option A:** Total Lung Capacity (TLC) is decreased in restrictive lung diseases due to decreased lung compliance and decreased lung volume.
**Option B:** Functional Residual Capacity (FRC) is decreased in restrictive lung diseases due to decreased lung volume and increased lung stiffness.
**Option C:** Forced Expiratory Volume in 1 second (FEV1) may be decreased in restrictive lung diseases due to decreased lung volume, but FEV1/FVC ratio can be normal or decreased.

**Clinical Pearl / High-Yield Fact**
In restrictive lung diseases, the patient's lung function can be preserved if the disease process is not severe, making it challenging to diagnose based on lung function tests alone.

**Correct Answer:** D.