Most parents who are generous are good parents, but some self-centered parents are also good parents. Yet all good parents share one characteristic: they are good listeners. If all of the statements in the passage are true, which one of the following must also be true? ['All parents who are good listeners are good parents.', 'Some parents who are good listeners are self-centered.', 'Some parents who are good listeners are not good parents.', 'Most parents who are good listeners are generous.']