Read the sentence. Much to the delight of the students, the faculty decided to enrich the curriculum by adding art to Tuesday mornings and art to Thursday mornings.

The correct answer to this open question is the following.

Here we just have a sentence, but not a question. It seems you forgot to include the question.

However, trying to help you, we did some research and found that the proper question is "Which part of the sentence contains an infinitive?"

If that is the case, then the correct answer is "to enrich."

Much to the delight of the students, the faculty decided to enrich the curriculum by adding art to Tuesday mornings and art to Thursday mornings.

In grammar, the infinitive form of verbs is known to be the basic form, as our elementary teachers taught us. It is when we use "to" before the verb.

Examples: to play, to eat, to run.