The imperfect subjunctive implies that the time of the subordinate clause is going on at the same time as the main verb.
The imperfect subjunctive implies that the time of the subordinate clause is going on at the same time as the main verb.
假设语气未完成式动词意谓附属子句动作发生的时间和主要子句动作发生的时间相同，亦即是附属子句的动作和主要子句的动作同时发生。