未知事件
He was an unknown painter one year ago. 一年前，他还是一个不为人知的画家。
The disease was practically unknown ten years ago but then it flared and spread like wild fire until it reached epidemic proportions. 这种疾病10年前几乎无人知晓，可它突然爆发象野火般迅速传播，直至流行甚广。
