未知事件
He was an unknown painter one year ago. 一年前，他還是一個不為人知的畫家。
The disease was practically unknown ten years ago but then it flared and spread like wild fire until it reached epidemic proportions. 這種疾病10年前幾乎無人知曉，可它突然爆發(fā)象野火般迅速傳播，直至流行甚廣。
