Correct answer:
c. cómica.
Both seria and cómica are adjectives that have opposite meanings. So seria means serious and cómica means funny. Recall that an adjective is a word that gives us more information about a noun or pronoun. Since we are talking about a woman, that is, a feminine singular noun, we must use these adjectives in feminine singular form and these two adjectives meets the requirements. Finally:
Daniela era seria. No, era cómica