able的名词形式是什么?

　　They overestimated his ability when they promoted him.

　　他们提拔他的时候高估了他的.能力。

　　Contestants were grouped according to age and ability.

　　参赛者按年龄和能力分组。

　　His outstanding ability earned him a place on the team.

　　他非凡的能力为他在队中赢得了一席之地。