It’s definitely es dudoso que vengan en tren, trust me I’m a native speaker
4. Esquiar
That means skiing. If you would chosen 1, it would mean singing, and you can sing anytime and not only winter. 2, it means riding a bike, and you definitely can't do that in winter. And 3, that would mean swimming, and I'm pretty sure nobody would want to swim when it's freezing cold outside.
