最近在看指考英文，綜合測驗有一題：
In certain situations such as in crowed subway cars or elevators, it is not al
ways possible for people to keep their _______ distance from others.
這一題答案是preferred，我有選對，但想請問在這裡preferring和preferred的差異是什
麼？
為什麼不能用preferring?
是因為距離是「被偏好的」嗎？
感謝