He has clearly demonstrated his commitment to the team's success.

demonstrated 是动词 demonstrate 的过去分词形式。demonstrate 由前缀 de-（表示"完全地"）和词根 monstr（来自拉丁语 monstrare，意为"展示"）组成，加上动词后缀 -ate，意思是"清楚地展示、证明"。在句中表示"已经清楚地展示出"的意思。