**Core Concept**
Biological agents, also known as biologics, are a class of medications derived from living organisms, such as bacteria, viruses, or yeast. They are used to treat various diseases, including autoimmune disorders, cancers, and infectious diseases. Biologics work by targeting specific molecules or pathways involved in disease pathology.

**Why the Correct Answer is Right**
Biologics can stimulate the immune system or suppress its activity, depending on the disease being treated. For example, monoclonal antibodies, a type of biologic, can bind to specific proteins on the surface of cancer cells, marking them for destruction by the immune system. Interferons, another type of biologic, can stimulate the immune system to produce antiviral proteins, helping to combat viral infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the characteristics of biological agents.
* **Option B:** This option is incorrect because it is too broad and does not specifically address the characteristics of biologics.
* **Option C:** This option is incorrect because it is not a characteristic of biological agents.

**Clinical Pearl / High-Yield Fact**
One important consideration when using biologics is their potential for immunogenicity, meaning they can stimulate an immune response against themselves. This can lead to the formation of antibodies against the biologic, reducing its efficacy over time.

**Correct Answer: C.**