**Core Concept**
The complement system is a group of proteins that work together to help clear pathogens from the body. It is an important part of the innate immune system and consists of multiple components that can be activated through different pathways.

**Why the Correct Answer is Right**
The terminal components of the complement system are C5b-9, also known as the membrane attack complex (MAC). When the complement cascade is activated, it leads to the formation of C5b, which then combines with C6, C7, C8, and multiple C9 molecules to form the MAC. This complex inserts into the membrane of the target cell, causing cell lysis and death. The MAC is the final and most potent step in the complement cascade, and its formation is crucial for the elimination of pathogens.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the classical pathway components (C1-C4) are not terminal components of the complement system.
**Option B:** Incorrect because the alternative pathway components (C3b, factor B, and factor D) are not terminal components of the complement system, although they play a crucial role in its activation.
**Option C:** Incorrect because the lectin pathway components (mannose-binding lectin and MASP) are not terminal components of the complement system, but rather contribute to the activation of the classical pathway.

**Clinical Pearl / High-Yield Fact**
The complement system plays a critical role in the defense against bacterial infections, particularly those caused by Neisseria species, such as Neisseria meningitidis and Neisseria gonorrhoeae. The MAC is the key effector molecule in this process, and its formation is essential for the elimination of these pathogens.

**Correct Answer:** C. C5b-9.