he must have had an accident,or he should have been here then
他一定出事故了,要不然他当时会在这儿了
语言点：
1.must have + 过去分词 这个结构用以对已经发生的事情作以肯定的推测,意为：想必已经.一定已经.
2.or 在此句相当于一个虚拟条件句.= If he had not had an accident
3.表示与过去事实相反,if 从句用had+ 过去分词（此句用or 表示了）,主句是：would/ should/ might/ could + have + 过去分词.此句是【should have been】