**Core Concept**
Infectious mononucleosis is caused by Epstein-Barr virus (EBV), leading to a characteristic clinical syndrome involving lymphocytosis, fever, and systemic symptoms. The disease manifests with a combination of fever, pharyngitis, and lymphadenopathy, often with glandular and mucosal involvement.

**Why the Correct Answer is Right**
Infectious mononucleosis commonly presents with **fever** (febrile illness), **glandular enlargement** (especially cervical lymphadenopathy), and **palatine petechiae** due to thrombocytopenia and capillary fragility. These features are hallmark signs of EBV infection, with petechiae arising from small vessel damage. The triad of fever, lymphadenopathy, and petechiae is frequently observed in clinical practice.

**Why Each Wrong Option is Incorrect**
Option A: Glandular involvement is a key feature, so this is not incorrect.
Option B: Febrile illness is a core feature, so this is not incorrect.
Option C: Palatine petechiae, though not universal, are a recognized sign, especially in severe cases.
Thus, all options are valid features, making "D. All of the above" correct.

**Clinical Pearl / High-Yield Fact**
Remember: "Mono" presents with **fever, pharyngitis, lymphadenopathy, and petechiae** — especially in adolescents and young adults. It is often misdiagnosed as strep throat; EBV testing and heterophile antibody detection are key.

✓ Correct Answer: D. All of the above