**Core Concept**
Bence Jones proteins are abnormal light chains of immunoglobulins that are excreted in the urine due to their small size and ability to pass through the glomerular filtration barrier. These proteins are a hallmark of certain plasma cell dyscrasias, such as multiple myeloma.

**Why the Correct Answer is Right**
Bence Jones proteins are derived from the variable regions of the light chains of immunoglobulins. Specifically, they are composed of either kappa (κ) or lambda (λ) light chains, which are produced by plasma cells. The production of excess light chains can lead to their accumulation in the urine, resulting in the presence of Bence Jones proteins.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Bence Jones proteins are not derived from heavy chains. Heavy chains are larger and do not pass through the glomerular filtration barrier.
**Option B:** This option is incorrect because Bence Jones proteins are not derived from complement proteins. While complement proteins can be involved in the pathogenesis of certain plasma cell dyscrasias, they are not the source of Bence Jones proteins.
**Option C:** This option is incorrect because Bence Jones proteins are not derived from fibrinogen. Fibrinogen is a coagulation protein that is not related to the production of Bence Jones proteins.

**Clinical Pearl / High-Yield Fact**
Bence Jones proteins can be detected in the urine using electrophoresis or immunofixation. The presence of these proteins is a critical diagnostic clue in the evaluation of patients with suspected plasma cell dyscrasias.

**Correct Answer:** D. Kappa (κ) or lambda (λ) light chains of immunoglobulins.