since then是用作时间状语的副词性短语,既可以用在陈述句也可以用在疑问句,如：
Your life must have seemed very ordinary since then.你的生活从那时起一定是非常平淡无奇的.【肯定句】
Your life can’t have seemed veryordinary since then. 你的生活从那时起不会是非常显得平淡无奇的.【否定句】
Can your life have seemed very ordinary since then? 你的生活从那时起会显得非常平淡无奇吗?【疑问句】
Since then I've been waiting on events. 自那以后,我就一直在观望事情的发展.【肯定句】
Since then I've not been waiting on events. 自那以后,我就一直都没在观望事情的发展.【否定句】
Have you been waiting on events since then? 自那以后,你一直在观望事情的发展吗?【疑问句】
