since then意为 "从那时以来",通常与动词的现在完成时连用,指从过去某一时刻起到现在为止的一段时间。
Since then 前后各接什么时态
Since then 前后一般接现在完成时,从那以后,现在完成时表示过去的某件事对现在还有影响, 现在完成时的标志性时间状语already , ever , never , yet , just , before, still , lately ,since , for a long time ,up to now, until,so far,in the last few years/weeks/mouths , till now,recently