1、challenge

挑战;难题

I like a big challenge and they don't come much bigger than this.

我喜欢大的挑战，而所有挑战中再没有比这更大的了。

The new government's first challenge is the economy.

新政府面临的第一个难题是经济问题。

(成功地)应对挑战，迎接挑战

The new Germany must rise to the challenge of its enhanced responsibilities.

一个崭新的德国必须迎接挑战，承担更多的责任。

They rose to the challenge of entertaining 80 schoolchildren for an afternoon.

他们一个下午成功接待了80名学童。

怀疑，质疑(真实性、价值、权威等)

Democratic leaders have challenged the president to sign the bill.

民主党领袖对总统签署这项法案提出了质疑。

The move was immediately challenged by two of the republics...

此项动议立即遭到其中两个共和国的反对。

2、call up

(给…)打电话

When I'm in Pittsburgh, I call him up.

我每到匹兹堡,都给他打电话。

He called up the museum.

他给博物馆打了电话。

(陆、海、空军)征召…入伍

Youngsters coming up to university were being called up.

快上大学的青年人受到征召。

The United States has called up some 150,000 military reservists.

美国已经征召了约15万名预备役军人。

选中,挑选(…参加运动队)

He is likely to be called up for Thursday's match against Italy.

他有可能被选中参加星期四对意大利的比赛。

3、step up

增加(数量等);提高(速度、强度等)

He urged donors to step up their efforts to send aid to Somalia.

他敦促各捐赠方加快速度将援助物资送往索马里。

Security is being stepped up to deal with the increase in violence.

正在加强安保工作以应对日益增多的暴力活动。