It must be hard for her, bringing up four children on her own.

她一个人抚养四个孩子一定很艰难。

《牛津词典》

During stages three and four (often called "deep sleep") , it is very hard to wake up a person.

在第三和第四阶段（通常称为“深度睡眠”），这时唤醒一个人是很难的。

youdao

It has a four-core CPU, an independent display card of 2G, a hard disk of 500G and a screen of 15.6 inches.

它配有一个四核 CPU，一个独立 2G 显卡，一个 500G 硬盘和15.6英寸屏幕。

youdao

Walking through these historic areas, visitors today might find it hard to believe that a deadly storm swept through the city over four years ago.

VOA: special.2010.01.22

It's great idea with a lot of hard work and then you work at it for year, two years, three years, four years, five years, six years, seven years, eight, nine, 10.

勤奋的工作，一年两年，三年,有或者更多，甚至10年，是很好的想法。

斯坦福公开课 - 微软CEO-Steve.Ballmer谈科技的未来课程节选

It seems hard to believe that it had been 62 years since the Americans had won Olympic gold in the four-man bobsled.

VOA: standard.2010.02.28

Though the Obamans certainly hit John McCain hard four years ago--running more negative ads than any campaign in history--what they intend to do to Romney is more savage.

WSJ: What's at Stake in Wisconsin

"I can't believe we fought so hard for four years and the result is this!"

CNN: STORY HIGHLIGHTS

Since he finished studying, Smith has pushed hard to get four major projects off the ground and sold.

BBC: The business of photojournalism