**Core Concept**
The question is testing the student's knowledge of the structure and function of Immunoglobulins (Igs), also known as antibodies. Specifically, it is inquiring about the role of IgD as a receptor for antigens.

**Why the Correct Answer is Right**
IgD is a type of antibody that plays a key role in the recognition of antigens. It acts as a receptor for antigens on the surface of B cells, a type of white blood cell. IgD is expressed on the surface of mature B cells and serves as a receptor for antigens, helping to trigger the activation of B cells and the initiation of an immune response. This process involves the binding of IgD to the antigen, which activates the B cell receptor complex, leading to the activation of the B cell and the production of antibodies.

**Why Each Wrong Option is Incorrect**
**Option A:** IgG is the most abundant type of antibody in the blood and plays a key role in the secondary immune response. However, it is not expressed on the surface of B cells as a receptor for antigens.

**Option B:** IgM is the first antibody produced in response to an antigen and is involved in the primary immune response. While it can bind to antigens, it is not expressed on the surface of B cells as a receptor.

**Option D:** IgE is involved in the allergic response and is not expressed on the surface of B cells as a receptor for antigens.

**Clinical Pearl / High-Yield Fact**
IgD is unique among the Immunoglobulins in that it is primarily expressed on the surface of mature B cells, where it serves as a receptor for antigens. This is in contrast to other Immunoglobulins, which are primarily secreted into the bloodstream or other bodily fluids.

**✓ Correct Answer: C. IgD**