Planning which dish to make first is the most challenging part of putting this party together.

Changing the way your business operates can be the most important - and challenging - part of the process.

Often, the most challenging part is to know what exactly the mistake or success consists in.

He was like a great actor, deeply immersed in the most challenging part of his career.

The questioning would be the most challenging part of it.

Still, the most challenging part of these operas isn't putting them up.

Next comes the most challenging part of her job: courting the homeowners.

"That is clearly the most challenging conceptual part of this program."

Someone asked what was the most challenging part of making a movie.

Hovering is the most challenging part of flying a helicopter.