**Core Concept**
Non-motile bacteria are a group of microorganisms that lack the ability to move. This characteristic is often associated with certain species of bacteria, which have adapted to their environment in various ways, such as adhering to surfaces or relying on other mechanisms for survival and reproduction.

**Why the Correct Answer is Right**
Non-motility in bacteria is typically due to the absence or dysfunction of flagella, which are the whip-like appendages responsible for their movement. In some cases, non-motile bacteria may have developed alternative mechanisms, such as pili or fimbriae, to facilitate attachment and colonization. For example, non-motile bacteria like *Escherichia coli* (E. coli) and *Staphylococcus epidermidis* have evolved to rely on their ability to form biofilms and adhere to surfaces.

**Why Each Wrong Option is Incorrect**
**Option A:** *Pseudomonas aeruginosa* is actually a motile bacterium that uses its flagella to move and colonize its environment.
**Option B:** *Bacillus anthracis* is also a motile bacterium, but it can form non-motile, spore-forming structures under certain conditions.
**Option C:** *Streptococcus pneumoniae* is a non-motile bacterium, but it is not the only example, and the question is asking for a more general category.

**Clinical Pearl / High-Yield Fact**
Non-motility can be an important characteristic in the identification and classification of bacteria, particularly in the context of infection and disease. Understanding the movement patterns of bacteria can help clinicians diagnose and treat infections more effectively.

**Correct Answer:** C. *Streptococcus pneumoniae*.