那是一个不幸的错误。

That was an ___unfortunate mistake.

很不幸，她丢了工作，就在她丈夫生病的时候。

It was so ___unfortunate that she lost her job just as her husband became ill.

很遗憾，他没能通知你关于会议的事。

It is ___unfortunate that he couldn't inform you about the conference.