乘地铁和乘飞机用介词表达除了by plane by subway还可以用in the subway

题目

乘地铁和乘飞机用介词表达除了by plane by subway还可以用in the subway
in the subway on the subway in the plane on the plane 到底用on 还是 in
我疑惑了，有没有明确的答案，还是俩都可以

答案

travel IN a private plane
travel ON a slow train