（1）他以他的生命为代价去帮助他的朋友.潜台词：他已经死了
------ He helped his friend(s) at the cost of his life.
（2）他以他的生命为代价去帮助他的朋友.潜台词：他还没死
------ He has been helping his friend(s) at the expense of his life.