He was very ill before he died.一般过去时,指一种状态：他死前病的很严重.
He had been very ill before he died.过去完成时,指一个状态在过去的某段时间内一直持续,：他一直病得很重,直到他死.�Ҿ�һ���ط�������After you left, we all missed you. After you had left, we all missed you. �����䶼��ȷ����ȷ�Ļ���Ϊ��˵��Ϊʲôһ����hadһ��û�����ڶ��仰����ȷ�ɡ���Ȼ����ǵڶ��仰��ʾ����ȥ������˼�����뿪�����Ƕ������㣬�뿪����ǰ��Ӧ���ǹ�ȥ�Ĺ�ȥΪʲôû��had�أ��뿪�������������������֮ǰ����Ϊ�뿪�ˣ�����������������뿪��left��,�Ǹ����ݵĶ�������Ҫ��ʾ�������Ѿ��뿪��һ����ʵ������Ҫ������Ѿ��뿪�ܾ���һ��״̬��You had left a month ��