[知 识 梳 理]　　　　　　　　　　　　　　　　　　　　　　 观察感悟(源于教材) Ⅰ.复习现在完成进行时 1．We ____________(excavate)here for many years and... 2．We ____________(excavate)layers of ash almost six metres thick，which suggests that they might have kept the fire burning all winter. 3．Well，we ____________(find)the bones of tigers and bears in the caves，and we think these were their most dangerous enemies.