**Core Concept**
Multiple myeloma is a type of blood cancer characterized by the proliferation of malignant plasma cells in the bone marrow. The disease is often associated with various biochemical abnormalities, including the production of abnormal proteins.

**Why the Correct Answer is Right**
The correct answer is related to the abnormal protein production in multiple myeloma. In this disease, the malignant plasma cells produce a monoclonal protein, also known as M protein, which can be detected in the blood or urine. The M protein can be composed of two types of immunoglobulins: light chains (Bence Jones proteins) or heavy chains. The presence of Bence Jones proteins in the urine is a hallmark of multiple myeloma.

**Why Each Wrong Option is Incorrect**
**Option A:** While anemia is a common complication of multiple myeloma, it is not a characteristic feature of the disease. Anemia in multiple myeloma is usually due to bone marrow infiltration by malignant cells.
**Option B:** Hypercalcemia is a common complication of multiple myeloma, but it is not the characteristic feature of the disease. Hypercalcemia in multiple myeloma is usually due to bone destruction by malignant cells.
**Option C:** While infections are a common complication of multiple myeloma, they are not a characteristic feature of the disease. Infections in multiple myeloma are usually due to immunosuppression caused by the disease.

**Clinical Pearl / High-Yield Fact**
Bence Jones proteins are a type of light chain protein that can be detected in the urine of patients with multiple myeloma. These proteins are produced by the malignant plasma cells and can be used as a diagnostic marker for the disease.

**Correct Answer: D. Bence Jones proteins**