地铁几号线的英语怎么说

地铁几号线的英语表达方式为"Line number"。来源是在英语中，"line"通常指交通工具的路线，而地铁就是一种交通工具，所以在英文中将地铁称为"subway line"或"metro line"。

例句：

"I usually take the subway to work, so I need to know which line to take." (我通常坐地铁上班，所以我需要知道哪条线路。)
"The subway system in this city is quite extensive, with multiple lines criss-crossing the city." (这个城市的地铁系统非常广泛，有多条线路穿过整个城市。)
"I'm trying to get to the airport, which line should I take?" (我想去机场，我应该坐哪条线路？)