他辞职的决定对所有人来说都无法解释。

His decision to resign was ___inexplicable to everyone.

由于某些无法解释的原因，尽管计划周全，项目还是失败了。

For some ___inexplicable reason, the project failed despite all the planning.

这个古老文明的消失对历史学家来说仍然无法解释。

The disappearance of the ancient civilization remains ___inexplicable to historians.