英语提问：这句话的时态不理解,
When the fire broke out in the basement,Tom had gone down to put out the fire immediately.（当地下室发生火灾时,汤姆立即下楼前去灭火.）时间状语从句火灾发生在前,主句汤姆灭火在后,我感觉主句和从句应该都用一般过去时.可原句是状语从句用一般过去时,主句用过去完成时,