"It was the most challenging thing I've done in my whole life," she said.

Einstein said, "I think it will be a challenging thing to do.

A child-genius is a challenging thing for an author to create, and I'm not convinced.

All you might wish for is that each had more challenging things to do.

To make things more challenging, most of the settlers had no prior farming experience.

The most challenging thing has been doing this for the first time.

"Navigation would be the challenging thing," a federal official said.

"Next to giving birth to my son, this has been the most difficult and challenging thing I have ever done, but so personally rewarding."

But he was onto larger, more challenging things as well.

"The challenging thing was, you never know what you did wrong," she said.