### Core Concept
The patient's symptoms of recurrent sore throat, severe neutropenia, and a total leucocyte count within the normal range suggest a condition involving abnormal neutrophil production or function. This condition may be related to autoimmune disorders, congenital defects, or infections affecting the bone marrow or peripheral blood.

### Why the Correct Answer is Right
The patient's presentation is consistent with **Chronic Neutropenia**, which is characterized by a persistent decrease in neutrophil count due to impaired production, increased destruction, or both. The differential count revealed severe neutropenia, indicating a significant reduction in neutrophil count. In this context, the correct answer involves a condition that affects the production or function of neutrophils.

### Why Each Wrong Option is Incorrect
**Option A:** This is incorrect because **Aplastic Anemia** involves pancytopenia, which is a reduction in all three blood cell lines (red blood cells, white blood cells, and platelets) due to bone marrow failure. While it may present with neutropenia, it is not the most likely diagnosis given the patient's specific presentation.

**Option B:** This is incorrect because **Follicular Lymphoma** is a type of non-Hodgkin lymphoma that primarily affects the lymphoid cells, not the neutrophil lineage. It may cause neutropenia indirectly through bone marrow infiltration, but this is not the primary diagnosis in this scenario.

**Option C:** This is incorrect because **Leukemia** involves abnormal proliferation of leukocytes, which can lead to neutropenia. However, the patient's presentation does not suggest leukemia as the primary diagnosis, as leukemia typically presents with an elevated total leukocyte count.

### Clinical Pearl / High-Yield Fact
In chronic neutropenia, patients are more susceptible to recurrent infections, particularly those caused by gram-positive bacteria and fungi. This is because neutrophils play a crucial role in defending against these pathogens.

### Correct Answer: C. Chronic Neutropenia