**Core Concept**
The complement system is a group of proteins that play a crucial role in the innate immune response, helping to eliminate pathogens from the body. The liver is the primary site of complement production, with the complement system being activated through three main pathways: the classical, alternative, and lectin pathways.

**Why the Correct Answer is Right**
Complement proteins, such as C3, C4, and C5, are synthesized in the liver and released into the bloodstream. The liver produces the majority of the complement components, which then circulate in the bloodstream and can be activated at the site of infection. The classical pathway is initiated by the binding of C1q to antibodies that have bound to the surface of pathogens, leading to the activation of C4 and C2. The alternative pathway is activated by the presence of bacterial cell wall components, such as lipopolysaccharides, and the lectin pathway is activated by the binding of mannose-binding lectin to carbohydrate moieties on the surface of pathogens.

**Why Each Wrong Option is Incorrect**
**Option A is incorrect** because while the spleen does filter the blood and remove pathogens, it is not the primary site of complement production.
**Option B is incorrect** because the kidneys do filter the blood and regulate electrolyte balance, but they are not directly involved in the production of complement proteins.
**Option C is incorrect** because the lungs are responsible for gas exchange and do not play a significant role in complement production.

**Clinical Pearl / High-Yield Fact**
The complement system plays a critical role in the elimination of pathogens from the body, and defects in the complement pathway can lead to increased susceptibility to infections.

**Correct Answer:** C