adj.出现于舞台上的;跑龙套;
例句:
Tourists go there to walk on the beach.
旅行者去那儿的海滩散步.
It is dangerous to walk on the thin ice.
在薄冰上行走是危险的.
The ice on the river is thick enough to walk on.
河上的冰已经禁得住人走了.