But the professor says it is difficult to find enough feathers from a single dinosaur to recreate all its colors.

VOA: special.2010.03.16

He says the actively changing nature of the Internet makes it difficult to stay current in studying its effects.

VOA: special.2010.01.28

Industry leaders, meeting this week in Malaysia, were told that their industry faces its most difficult situation ever.

VOA: special.2009.06.13

The recovery of the Stardust capsule was difficult because of its high reentry speed.

VOA: special.2009.09.30

But the timing of its opening in January has been difficult.

VOA: special.2010.03.31

Crystal says the dynamic nature of the Internet makes it difficult for comprehensive analysis of its effects to stay up-to-date.

VOA: standard.2010.01.16