同义词是hard，例如：
1、People tend to work hard at this stage of life.人在这个人生阶段往往发奋努力。
2、Her job is hard work， but the pay is good.她工作虽辛苦，但薪水不低。
3、When I left they were all still hard at it.我离开的时候他们都还在努力工作。
4、.You think you're really hard， don't you?你是不是以为自己真的很勇猛
