Final answer:
Cosima Liszt was the third illegitimate child of Marie, Countess d'Agoult, and Franz Liszt, named after St. Cosmas, which corresponds to option c) Cosima.
Step-by-step explanation:
The child of Marie, Countess d'Agoult, and Franz Liszt, who was named after St. Cosmas, is option c) Cosima. Cosima Liszt went on to become noteworthy in her own right, marrying the composer Richard Wagner.
Marie, Countess d'Agoult, had three illegitimate children with Franz Liszt: Daniel, Blandine, and Cosima. The name that corresponds with St. Cosmas, as indicated in the multiple-choice options provided in the question, is most closely associated with 'Cosima.'