**Core Concept**
Chronic Myeloid Leukemia (CML) is a type of myeloproliferative neoplasm characterized by the uncontrolled proliferation of mature granulocytes and their precursors. The size of splenomegaly in CML patients is an important prognostic indicator, reflecting the extent of bone marrow involvement and disease burden.

**Why the Correct Answer is Right**
The size of splenomegaly in CML patients correlates with the severity of disease, with larger spleens indicating more advanced disease. This is because the spleen is a major site of granulocytic proliferation and sequestration in CML. The spleen's size can be used as a surrogate marker for the extent of bone marrow involvement, which in turn affects the patient's prognosis. The Ph+ chromosome, resulting from the BCR-ABL fusion gene, is a hallmark of CML, but it is not directly related to the size of splenomegaly.

**Why Each Wrong Option is Incorrect**
**Option B:** Phagocytic activity of WBC is actually increased in CML, not reduced, due to the excessive production of granulocytes and their precursors.

**Option C:** Sudan black stain is not specific for myeloblasts in CML. While it can stain myeloblasts, it also stains other types of cells, including granulocytes and monocytes.

**Option D:** Myeloblasts, granuloblasts, and lymphoblasts in CML are all Ph+ chromosome-positive due to the BCR-ABL fusion gene. Remission in CML does not result in the loss of the Ph+ chromosome.

**Clinical Pearl / High-Yield Fact**
The size of splenomegaly in CML patients is an important prognostic indicator that can be used to guide treatment decisions. A larger spleen size may require more aggressive treatment, including splenectomy or targeted therapy.

**✓ Correct Answer: A. Size of splenomegaly indicates prognosis**