Final answer:
The most appropriate verb to fill in the blank is 'estoy'.
Step-by-step explanation:
The most appropriate verb to fill in the blank is estoy. The correct sentence would be 'Yo estoy barriendo el piso.' In this case, 'estoy' is the first person singular form of the verb 'estar' in the present tense, which matches with the subject 'yo' (I). This sentence means 'I am sweeping the floor'.
Learn more about Verb conjugation in Spanish