It's quite simply the most challenging material for any actor to get to grips with.

A principal laments that "many teachers can't write," let alone teach challenging material.

The specific proportions of the different types of metal in steel can make it a very challenging material to work with.

I'll bet that, given more challenging material, they and the readers would have had just as much fun.

The strong showing may well be the result of the new Regents' math curriculum that gives students more challenging material in early grades.

This is excellent, challenging material for middle-grade and older children and adults.

But you're used to doing challenging material on stage.

She picks challenging material, usually by neophyte directors, and then stands by them.

NaTe is a challenging material to handle because it is very sensitive to air.

Congratulations to those who take on challenging material and stand up to the injustice of censorship.