**Core Concept**
The question is testing the knowledge of the radiographic signs associated with a specific condition affecting the mediastinum and lung fields. The "double shadow" and "straightening of the left main bronchus" are classic radiographic findings that can help diagnose a particular condition.

**Why the Correct Answer is Right**
The correct answer is linked to the presence of a **mass** or **tumor** in the mediastinum, specifically the right paratracheal region. The "double shadow" is due to the overlapping of the right atrial border and the tumor, creating a double contour. The "straightening of the left main bronchus" occurs because the tumor displaces the trachea to the right, causing the left main bronchus to become more vertical.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the radiographic findings associated with the condition. While a mediastinal mass can cause a variety of radiographic abnormalities, the specific combination of a double shadow and straightening of the left main bronchus is more characteristic of a different condition.
* **Option B:** This option is incorrect because it does not provide a clear description of a radiographic finding. The term " mediastinal contour" is too vague and does not accurately describe the specific signs mentioned in the question.
* **Option C:** This option is incorrect because it does not accurately describe the condition. While a mediastinal mass can cause a variety of symptoms, the specific combination of a double shadow and straightening of the left main bronchus is more characteristic of a different condition.

**Clinical Pearl / High-Yield Fact**
When interpreting chest radiographs, it is essential to look for specific radiographic signs that can help diagnose mediastinal masses. The combination of a double shadow and straightening of the left main bronchus is a classic finding associated with a right paratracheal mass.

**Correct Answer:** C.