**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. It consists of over 20 proteins that work together to form a cascade of reactions, ultimately leading to the destruction of foreign substances.

**Why the Correct Answer is Right**
The complement system is a complex network of proteins that interact with each other in a highly regulated manner. It can be activated through three different pathways: the classical pathway, the alternative pathway, and the lectin pathway. Once activated, the complement system forms a membrane attack complex (MAC) that creates pores in the cell membrane of target cells, leading to cell lysis and death. The MAC is composed of several proteins, including C5b, C6, C7, C8, and multiple copies of C9.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the chemical nature of complement.
**Option B:** This option is incorrect because it does not accurately describe the chemical nature of complement.
**Option C:** This option is incorrect because it does not accurately describe the chemical nature of complement.

**Clinical Pearl / High-Yield Fact**
The complement system plays a critical role in the pathogenesis of various diseases, including autoimmune disorders, such as systemic lupus erythematosus (SLE), and infections, such as meningitis. Understanding the chemical nature of complement is essential for developing effective therapeutic strategies for these conditions.

**Correct Answer: C. Protein. Complement is a group of proteins that work together to eliminate pathogens from the body.**