The correct answer is D. are promoted at the festival
Step-by-step explanation:
In a sentence, the complete predicate includes the main verb and all the words after it that commonly act as a complement or object of the action, this means the complete predicate follows the subject and describes what is exactly happening. According to this, in the sentence presented the subject would be "Welsh language, literature, music, and culture" because this is the agent and thus, the complete predicate would include the actions "are promoted" and the words "at the festival" that complete the meaning of the action.