Light rail trains also operate at grade, instead of relying on elevated tracks and tunnels.轻轨列车也在同一平面上运行，而不用依靠高架轨道和隧道。All the planets orbit the Sun in roughly the same plane, round its equator.所有的行星大致在同一平面上绕太阳赤道运转。The door is flush with the walls.门与墙壁在同一平面上。