Answer:
it uses passive voice because they are trying to point out the main part. it wanted to point out that the flowers were trimmed by jill every month so it pointed out that jill trims the flowers every month
Step-by-step explanation:
In English, the passive voice is used when we want to emphasize certain part of the sentence, such as the person or the thing affected by the action. In this case, the writer of the sentence wants to focus attention on the object (the flowers) by putting them at the beginning of the sentence, thus making it the subject (and the most important component of the sentence).