主线；主静脉
nbsp; The train moved slowly south through flat, drab mainline scenery. 火车穿过干线两侧风景单调乏味的地区，缓缓地向南驶去。
The train moved slowly south through flat, drab mainline scenery. 火车穿过干线两侧风景单调乏味的地区，缓缓地向南驶去。
n.main line 干线列车
