it was reported that 115 miners ---in the flooded mine for eight days were pulled out alive at last.

it was reported that 115 miners 【trapped】in the flooded mine for eight days were pulled out alive at last.
你的问题这样理解也许容易些：
1、划分句子成分：
主体句子结构
【it形式主语】【 was reported被动式谓语】【 that 115 miners trapped in the flooded mine for eight days were pulled out alive at last 主语从句】.
从句结构：
【115 miners 主语】【trapped in the flooded mine for eight days 过去分词短语,后置定语】【 were pulled out谓语】【 alive 状语】【at last状语】
2、关键规律运用：一个简单句中,不能同时存在两个非并列的谓语动词.
所给句子中,后面有一个被动式谓语动词短语【were pulled out】,句子中间也没有并列连词,因此,不能再有谓语动词,因此,可以反正：前面需要填的词只能是【非谓语动词】；
又因为,115 miners【 矿工】与【困住】这个动作是【矿工被困】,即【被动语态】,因此,只能使用【过去分词表被动】,而不能用谓语动词【were trapped】.
3、替换理
过去分词（短语）作定语,相当于定语从句：
it was reported that 115 miners 【who were trapped】in the flooded mine for eight days were pulled out alive at last.
4、分析得出的结论：
看句子中所用的词,需要注意句子结构和成分.所给从句中,句子的位于已经给出在后面,又不是并列句,因此,不能再使用谓语动词,只能使用【非谓语动词】；也可以替换为定语从句,从句中使用谓语动词.
祝你开心如意!