孩子们从篱笆上的一个开口爬了过去。

The children crawled through an ___opening in the fence.

水被允许通过大坝上的一个开口流出。

The water is allowed to flow through an ___opening in the dam.

探险者们在洞穴墙壁上发现了一个狭窄的开口。

The explorers found a narrow ___opening in the cave wall.