They had already had breakfast before they arrived at the ho

They had already had breakfast before they arrived at the hotel.
这里第一个had是过去完成时,指明时间的先后顺序
第二个had是实义动词,在这里可以 翻译为"吃"
Most of the quest had left when he arrived at the party.
这个句子翻译为:当他到达派对的时候,大多数客人(已经)离开了.(离开的原因未知)
注意:主句中had后所接的动作 发生在从句的动作之前.有先后关系.
Most of the quest left when he arrived at the party.
这个句子翻译为:当他到达派对的时候,大多数客人就离开了.(离开的原因是因为他来了)
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