他的行为完全无法解释，让我们都感到困惑。

His behavior was completely ___unaccountable, leaving us all confused.

这些决定是由一个不负责任的委员会做出的。

The decisions were made by an ___unaccountable committee.

他突然感到一阵莫名的悲伤，尽管周围一切都很美好。

He felt an ___unaccountable sadness suddenly, though everything around him was fine.