他们正在计划一次前往北极的远征，以研究气候变化。

They are planning an ___expedition to the North Pole to study climate change.

我们学校的登山之旅既充满挑战又很有趣。

Our school ___expedition to the mountains was both challenging and fun.

这次科学考察队在热带雨林里发现了新的物种。

The scientific ___expedition discovered new species in the rainforest.