He looked gloomy and troubled.
他看上去有些忧愁不安。（省略并列连接词）
As it is late, you had better go home.
时间不早了，你最好回家去吧。（省略表示原因的连接词）
If winter comes, can spring be far behind?
冬天来了，春天还会远吗？（省略表示条件的连接词）
If I had known it, I would not have joined in to.
早知如此，我就不参加了。（省略表示条件的连接词）
John rose gloomily as the train stopped, for he was thinking of his ailing mother.
火车停了，约翰郁郁地站了起来，因为他想起了病中的母亲。（省略表示时间的连接词）
