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、concentrate

全神贯注;集中（心思）

It was up to him to concentrate on his studies and make something of himself.

是否能专心学习并取得一定成就要靠他自己。

Water companies should concentrate on reducing waste instead of building new reservoirs.

自来水公司应该集中精力减少水浪费，而不是修建新水库。

使集中;使汇集

Italy's industrial districts are concentrated in its north-central and north-eastern regions.

意大利的工业区集中在该国中北部和东北部地区。

Most development has been concentrated in and around cities.

土地开发主要集中在城市及周边地区。