Final answer:
The urethral mucosa is primarily lined with transitional epithelium, which allows for changes in thickness as the bladder fills and empties.
Step-by-step explanation:
The urethral mucosa is lined with two types of epithelium: the proximal two-thirds with transitional epithelium and the distal third with mucus-secreting epithelium.
Transitional epithelium is specialized for the urinary system, where it can change its thickness as the urinary bladder fills and empties.
In the relaxed, empty bladder, the epithelial layer is thicker and cells appear to be stacked on top of one another. As the bladder fills, the layer unfolds and expands which makes the epithelium thinner.
Therefore, answering the student's question, the type of epithelium that lines the urethral mucosa is c. transitional epithelium.