他打电话说他在公共汽车上，几分钟后就到。

He called to say he's ___on the bus and will be here in a few minutes.

我们在渡轮上过河时玩得很开心。

We had a great time ___on the ferry crossing the river.

我更喜欢坐火车旅行，因为可以看风景。

I prefer traveling ___on a train because I can see the scenery.