The leader begins to rely on these individuals to help with especially challenging tasks.

Eating, drinking and using the bathroom are especially challenging activities for astronauts in orbit.

After the windstorm the sea was quiet for a while, never exactly tranquil but not especially challenging, either.

This category is especially useful for solving especially challenging problems.

This was especially challenging because it provided great scope to demonstrate imagination and intelligence.

But businesses with global brands, even the most highly regarded ones, face an especially challenging climate now.

That will make international travel especially challenging, with exchange rates going strongly against the dollar, he said.

Mind you, not all those tasks were especially challenging, but that wasn't the point.

The courthouse, built in 1975, presents an especially challenging security situation because its outside walls are glass.

This will be especially challenging because governance in the ocean is still embryonic.