The M-ATVs are also a major logistical challenge. The Pentagon transports them by air in order to meet the high demand, adding a 10-percent premium to the vehicle's cost.

VOA: standard.2010.08.01

So it was an opportunity for them to challenge themselves.

对他们来说,这是挑战自我的机会。

麻省理工公开课 - 媒体、教育、市场课程节选

- Part of the challenge is speed, too, how quickly you can get these answers in terms of getting them in on time.

部分困难也会来自于速度，你多快能做出答案,能否在规定的时间做完。

麻省理工公开课 - 化学原理课程节选

"There's a lot of technical terms in aviation and getting those translated properly and getting transmitted to them in a timely manner, especially when in flight, is a huge challenge.

VOA: standard.2009.12.13

There really can't be a challenge to them from the state itself.

绝对统治者不会允许在国内,有任何对于他们权威的挑战

耶鲁公开课 - 欧洲文明课程节选

The challenge is about all of them.

挑战在于包括所有这些。

麻省理工公开课 - 媒体、教育、市场课程节选