An infinitive is the basic form of the verb without a subject. When it is used in a sentence, it is preceded by "to". The correct answer is the one with a verb. To test it out just ask yourself if you can use it with the subject I after dropping "to". I enrich? Yes! Check, it's right. You can't say I the delight or I Tuesday mornings. The rest of the options are prepositional phrases because they start with the preposition to and end in a noun (person, place, thing, or idea).
