You are answering a USMLE-style medical question. Question: A 30-year-old female presents to her primary care provider complaining of 4 days of fever, malaise, dyspnea, and productive cough and has recently developed pleuritic chest pain. Her past medical history is notable for asthma and takes albuterol as needed. She does not smoke but drinks alcohol socially. Her family history is notable for cystic fibrosis in her paternal uncle and interstitial lung disease in her paternal grandfather. Her temperature is 101°F (38.3°C), blood pressure is 115/75 mmHg, pulse is 110/min, and respirations are 21/min. Rales are noted in the right lower lung, and a chest radiograph demonstrates focal consolidation in the right lower lung lobe. After initiating the appropriate treatment, she agrees to take part in a study assessing the immune response to lung infections. A protein is identified in her serum that is thought to be elevated in response to her condition. An amino acid sequence at the carboxy terminus of the protein is isolated and a fluorescent marker is added to the sequence. This labeled sequence is subsequently added to a gel containing a protein isolated from the cell surface of the patient’s own neutrophils and macrophages and subsequently labeled with another fluorescent marker. The sequence binds strongly to this protein as evidenced by increased fluorescence in the gel. What process does this sequence typically undergo in immunocompetent individuals? Options: A) Random assortment B) Random nucleotide addition C) VDJ recombination D) Isotype switching Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.