Final answer:
Thomas Eakins was influenced by scientific anatomy in his selection of subject matter, as seen in The Gross Clinic, highlighting his dedication to psychological intensity and scientific realism. Therefore, the correct option is c.
Step-by-step explanation:
An influence on Thomas Eakins's selection of subject matter was his dedication to scientific anatomy. Eakins was known for his commitment to psychological intensity and scientific realism, which is evident in his methodical approach to portraying honest details of form, depth, and proportion. This is demonstrated in his celebrated work The Gross Clinic, where he meticulously crafted a visual record of the individuals present in a medical amphitheater. His works often reflect a focus on the accurate human form and the integration of medical and scientific themes.