**Core Concept**
The complement system is a group of proteins that work together to enhance (complement) the ability of antibodies and phagocytic cells to clear pathogens from an organism. Immunoglobulins (antibodies) play a crucial role in activating the complement system through a process called antibody-dependent complement activation.

**Why the Correct Answer is Right**
When an antibody binds to its specific antigen, it can bring about a conformational change that exposes the Fc region of the antibody. The Fc region of the antibody serves as a binding site for the complement component C1q, a protein that initiates the classical pathway of complement activation. This binding of C1q to the Fc region of the antibody is a critical step in the activation of the complement system. The classical pathway is one of the three pathways of complement activation, the others being the lectin pathway and the alternative pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not applicable to the question.
**Option B:** This option is not a correct location for complement attachment to immunoglobulin.
**Option C:** This option is not the correct location for complement attachment to immunoglobulin.

**Clinical Pearl / High-Yield Fact**
The complement system plays a crucial role in the innate immune response, providing immediate defense against pathogens. It also works in conjunction with the adaptive immune response, enhancing the ability of antibodies and phagocytic cells to clear pathogens from the body.

**Correct Answer:** C. Fc region of the antibody.