responsibility主观上的责任，主动担当的职责。
duty客观的职责，一般是强制的职责。
The state has a duty to protect its citizens against external enemies.
国家有义务保护本国公民不受外敌侵犯。
A policeman was injured in the line of duty yesterday.
昨天有一名警察在执行公务时受伤。
He finally handed over his responsibility for the company last year.
他终于在去年交出了公司的职务。
