You are answering a USMLE-style medical question. Question: A 47-year-old woman with metastatic breast cancer who is undergoing chemotherapy comes to the physician for a follow-up exam. She reports extreme fatigue since beginning her chemotherapy regimen. Her pulse is 98/min, respirations are 16/min, and blood pressure is 132/84 mm Hg. Her hemoglobin is 10.4 g/dL, leukocyte count is 800/mm3 with 5% monocytes, and platelet count is 50,000/mm3. The patient is started on a new medication. One week later, serum studies show a hemoglobin of 10.6 g/dL, a leukocyte count of 2,000/mm3 with 2% monocytes, and a platelet count of 56,000/mm3. Which of the following drugs is the most likely cause of these findings? Options: A) Aldesleukin B) Interferon beta C) Filgrastim D) Romiplostim Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.