mercy的形容詞和名詞是？

　　例句：

　　They showed no mercy to their hostages.

　　他們對人質絲毫不講仁慈。

　　It's a mercy she wasn't seriously hurt.

　　幸運的是她傷勢不重。

　　God have mercy on us.

　　上帝憐憫我們吧。