用hardly……when时,主句中的动词若是行为动词则必须用过去完成时,从句这时是否一定要用一般过去时?

是的
Hardly had the game begun when it started raining.
比赛刚刚开始就下起雨来.
Hardly/Scarcely had we arrived,when it began to rain.
我们刚一到就下起雨来了.
Hardly had I opened the door when he told me.
我刚开开门,他就告诉了我.
再问： This morning I had hardly got to my school when at began to rain.这句话里when 引导的是什么从句？
再答： 这整个其实是个并列句， when 在这里不是从属连词，而是并列连词“其时”“就在这时” 所以，前后其实是并列关系的，不是什么从句
再问： 既然不是从句，为什么下面的解释中有“主句”的说法？是不是言外之意when 引导的是从句？ 使用hardly－ when时，主句中的动词若是行为动词则必须用过去完成时，when有时可改用before．如：中学生英语He had hardly finished the article when the light went out．他刚写完论文，灯就熄了。若把hardly放于句首，主句要倒装。如：Hardly had I finished eating when he came m．我刚吃完他就进来了。
再答： 你这种解释我见过，但我不认同。我相信第二种解释。 就以你这个句子为例： 要说时间关系，其实前一部分是为后一部分作铺垫的。 This morning I had hardly got to my school when it began to rain =As soon as I got to my school this morning, it began to rain. =The moment I got to my school this morning, it began to rain.