Books are easy to start, too, and they pose a similar challenge.

Today they pose a risk and a challenge for every country.

But never before has getting it right posed such a challenge.

It poses a major challenge for the local water board.

The single market poses new challenges for those in education and training.

That poses challenges enough for the rest of the world.

Those pose challenges to society that are different from what came before.

In addition, poor water quality continues to pose a challenge to environmental and human health.

However, the real challenge posed by the report is not scientific.

Yet changing political and security forces in the region pose a challenge to American policy.