Hypomimia refers to a reduced ability to express emotions through facial movements, specifically a deficit in facial expressions or gestures. It is commonly seen in conditions like Parkinson’s disease or severe depression, where emotional expression is diminished. While options A, B, and D relate to other cognitive or motor deficits (e.g., copying, execution, speech), hypomimia specifically targets **facial expression**. Option D, fluent speech deficit, relates to aphasia or language disorders, not emotional expression.

✓ Correct: C. Deficit of expression by gesture