Zhè / tiáo / tiě / lù / chuān / guò / shān / dì / shí / xū / yào / kāi / wā / hěn / cháng / de / lù / qiàn这条铁路穿过山地时,需要开挖很长的路堑。When the railway crosses the mountains, a long cutting needs to be excavated.