我们徒步跋涉了三天才穿过沙漠。

We ___trekked for three days to cross the desert.

他们计划进行一次为期三天的徒步旅行穿越森林。

They planned a three-day ___trek through the forest.

我们计划周末去森林里徒步旅行。

We're planning to ___trek through the forest this weekend.