**Core Concept**
The complement system is a crucial part of the innate immune response, which helps eliminate pathogens from the body. Both the antibody-dependent (classical) and antibody-independent (alternative and lectin) pathways converge on a key component, ultimately leading to the formation of the membrane attack complex (MAC) and the elimination of pathogens.

**Why the Correct Answer is Right**
The classical pathway is initiated by the binding of C1q to antibody-antigen complexes, leading to the activation of C1r and C1s. This cascade results in the activation of C4 and C2, forming C4b2a (C3 convertase). The alternative pathway is initiated by the spontaneous hydrolysis of C3, resulting in the formation of C3b. The lectin pathway is initiated by the binding of mannose-binding lectin (MBL) to carbohydrate patterns on microbial surfaces, leading to the activation of MASP-2 and the formation of C4b2a (C3 convertase). Both pathways converge on C3, which is cleaved into C3a and C3b, further activating the complement cascade.

**Why Each Wrong Option is Incorrect**
**Option A:** While C5 is a key component in the formation of the membrane attack complex (MAC), it is not the point of convergence for both the classical and alternative pathways.
**Option B:** C2 is a component of the classical pathway's C3 convertase, but it is not the point of convergence for both pathways.
**Option C:** C4 is a component of the classical pathway's C3 convertase, but it is not the point of convergence for both pathways.

**Clinical Pearl / High-Yield Fact**
The complement system plays a critical role in the elimination of pathogens, and its dysregulation can lead to various diseases, including autoimmune disorders and infections. Understanding the complement cascade is essential for clinicians to diagnose and manage these conditions effectively.

**Correct Answer:** C. C3.