by ship or plane与by ship or by plane

Shall we go bybus or train?

Shall we go bybus or by train?

哪句对？还是两句都对？

两个说法都对（省略后面一个 by 的表达不如用两个by 的使用方法更正式）：

Shall we go by bus or train?

Shall we go by bus or by train?

大家坐公共汽车去还是坐火车去?

又如：

You can freight your belongings by air or sea. 你可把东西经空运或海运运去。

One can travel there by ship or plane. Mostpeople choose the latter. 坐船或乘飞机去均可，大家多取后者。

Whether we go by bus or train, it’ll take at least six hours. 不管大家是乘公共汽车还是坐火车，至少得花六小时。