Okay, let's tackle this question. The user is asking about a CD marker specific for the myeloid series. First, I need to recall the key CD markers associated with different blood cell lineages. The myeloid lineage includes cells like granulocytes, monocytes, and their precursors.

I remember that CD34 is a common marker for hematopoietic stem cells, which are multipotent, so that's not specific to myeloid. CD19 is for B cells, which are part of the lymphoid lineage. CD13 and CD33 are markers I've heard are associated with myeloid cells. Specifically, CD33 is a well-known myeloid marker, expressed on myeloid blasts and some mature cells. CD13 is also present on myeloid cells, but maybe CD33 is more specific?

Wait, the question is about the marker that's specific. CD33 is expressed on myeloid cells, including acute myeloid leukemia blasts. CD13 might be present on other cells too, like platelets. So CD33 is more specific. Let me verify. Yes, CD33 is a member of the sialic acid-binding immunoglobulin-like lectin family and is specifically expressed on myeloid cells. CD13 is also myeloid but maybe not as specific. CD14 is for monocytes, but monocytes are part of myeloid. However, CD14 is more specific for monocytes/macrophages. But the question is about the myeloid series in general. So CD33 is the key marker here.

Looking at the options, the correct answer should be CD33. The other options like CD34 (stem cells), CD19 (B cells), CD14 (monocytes) are not specific to the entire myeloid lineage. So the correct answer is CD33.

**Core Concept**
The question tests knowledge of lineage-specific cluster of differentiation (CD) markers in hematopoiesis. Myeloid cells include granulocytes, monocytes, and their precursors, with **CD33** and **CD13** as key markers. Specificity depends on lineage commitment and differentiation stage.

**Why the Correct Answer is Right**
**CD33** is a type I transmembrane receptor expressed on **all myeloid blasts and mature myeloid cells**, including monocytes, granulocytes, and macrophages. It is absent on lymphoid cells, making it a hallmark of the myeloid lineage. CD33 binds sialic acid and modulates immune responses, serving as a diagnostic target in acute myeloid leukemia (AML).

**Why Each Wrong Option is Incorrect**
**Option A:** *CD34* marks hematopoietic stem cells and is present in both myeloid and lymphoid lineages, lacking specificity.
**Option B:** *CD19* is a B-cell-specific marker (lymphoid lineage), not myeloid.
**Option C:** *CD14* is restricted to monocytes/macrophages, a subset of myeloid cells, not the entire series.

**Clinical Pearl / High-Yield Fact**
CD33 is a **gold standard** myeloid marker used in flow cytometry for AML

✓ Correct Answer: C. CD99