Factor present in final common terminal complement pathway

**Core Concept**
The final common terminal complement pathway involves the assembly of the membrane attack complex (MAC) that forms pores in cell membranes, leading to cell lysis. This pathway is crucial for eliminating pathogens from the body.

**Why the Correct Answer is Right**
The correct answer is a component of the terminal pathway that interacts with C9 to form the MAC. C9 polymerizes to create an oligomeric structure that inserts into cell membranes, leading to cell lysis. The terminal pathway is initiated by the C5b-9 complex, which recruits C9 molecules to form the MAC.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a component of the terminal complement pathway.
**Option B:** This option is incorrect because it is involved in the classical pathway, not the terminal pathway.
**Option C:** This option is incorrect because it is involved in the lectin pathway, not the terminal pathway.

**Clinical Pearl / High-Yield Fact**
Recall that the terminal complement pathway is responsible for the formation of the MAC, which is the primary mechanism of cell lysis in the complement system.

**Correct Answer:** C. C9