**Core Concept**
The complement system is a group of proteins that plays a crucial role in the innate immune response, helping to eliminate pathogens from the body. One of its key functions is to induce cell lysis, or cell death, through the formation of a membrane attack complex (MAC).

**Why the Correct Answer is Right**
The correct answer is associated with the terminal pathway of the complement system, specifically the formation of the MAC. This complex is composed of several proteins, including C5b, C6, C7, C8, and multiple C9 molecules. The MAC inserts itself into the cell membrane of the target pathogen, disrupting its osmotic balance and ultimately leading to cell lysis. This process is mediated by the enzyme C5-convertase, which cleaves C5 into C5a and C5b, initiating the formation of the MAC.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because C1q is involved in the classical pathway of complement activation, not the terminal pathway responsible for cell lysis.
**Option B:** Incorrect because C3b is a key component of the opsonization process, marking pathogens for phagocytosis rather than inducing cell lysis.
**Option C:** Incorrect because factor B is involved in the alternative pathway of complement activation, which also does not directly lead to cell lysis.

**Clinical Pearl / High-Yield Fact**
The complement system plays a critical role in the innate immune response, but its dysregulation can lead to various diseases, including autoimmune disorders and inflammatory conditions.

**Correct Answer:** C. C9. C9 is a critical component of the MAC, which induces cell lysis through the terminal pathway of the complement system.