Cassatt spent her life working to change traditional beliefs about art and a woman's role in society.

VOA: special.2009.07.12

There have been fundamental changes through time that make the role of the central bank evolve and change through time.

试图保持系统的稳定,随着时间的发展，基本的改变发生,使得中央银行的角色演变。

耶鲁公开课 - 金融市场课程节选

Scientists at CSIRO, Australia's government-funded scientific research institute, say that climate change has played a role in the increase.

VOA: standard.2009.11.09

But nature plays a role as well. As for climate change, severe water shortages are predicted to affect between 75 and 250 million people by 2020.

VOA: standard.2010.03.29