Final answer:
The appropriate imperfect verb to fill in the blank is 'me cepillaba.'
Step-by-step explanation:
The appropriate imperfect verb to fill in the blank is B. me cepillaba. The sentence translates to 'While I was brushing my teeth, the water was shut off.' The verb 'cepillaba' is in the imperfect tense, which is used to describe ongoing or habitual past actions. In this case, it indicates that the action of brushing teeth was happening in the past.
Learn more about Imperfect verb usage in Spanish