题目内容：

for hundreds of years ,st.bernard dogs have saved the lives of travellers crossing the dangerous pass.这句话中 for

优质解答

从整句话的意思来看,for引的是完成时态,表示持续的状态.
如果不理解的话,你可以把for hundreds of years移到句末,也就是
st.bernard dogs have saved the lives of travellers crossing the dangerous pass for hundreds of years.这样我想你就好理解了.
而原句是想强调时间的长,才把其提前的.