However, certain challenges may not require the models at all.

This challenge has 20 questions, requires Flash 5 and takes 10 minutes.

The challenge of increasing international competition requires an appropriate response.

Each challenge will require the use of a team's timeout.

We are all agreed that this new challenge requires prompt action to be taken.

A challenge, if it were to occur, would require a major issue and a trigger.

The challenge later requires them to walk next to models who are 5'10" and above.

The challenge could require a new solution to an existing problem that had been ignored.

And for decades, we have failed to act with the sense of urgency that this challenge requires.

The social challenge required decisive and substantial response within Google.