**Core Concept**
The question is testing knowledge of the anatomical distribution of lymph nodes in the mediastinum, specifically in relation to the pathology of Infectious Mononucleosis (IMN). IMN is caused by Epstein-Barr virus (EBV) and primarily affects the lymphoid tissues, leading to lymphadenopathy.

**Why the Correct Answer is Right**
Infectious Mononucleosis typically involves the lymph nodes in the upper anterior mediastinum, particularly those surrounding the thymus. This is due to the thymus being a major site of EBV replication and the resultant lymphoid response. The lymph nodes in this region, such as the parasternal nodes, become enlarged and painful, characteristic of IMN.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct group of lymph nodes affected by IMN.
* **Option B:** This option is incorrect because it does not accurately describe the typical lymph node involvement in IMN.
* **Option D:** This option is incorrect because it is not the correct group of lymph nodes typically involved in IMN.

**Clinical Pearl / High-Yield Fact**
In addition to the upper anterior mediastinum, lymphadenopathy in IMN can also involve the cervical and supraclavicular lymph nodes due to the spread of EBV-infected cells through the lymphatic system.

**Correct Answer: C. The correct answer is the group of lymph nodes in the upper anterior mediastinum.