The phrase "a challenging material" is not correct in standard written English.
It should be "challenging materials" if referring to multiple types or "a challenging material" if referring to a single type, but "material" is typically uncountable in this context.
Example: "The course includes a challenging material that requires critical thinking and problem-solving skills."
Alternatives: "a difficult subject" or "a tough resource."
There is more lignin in softwoods (for example, spruce) than in hardwoods (for example, willow) or agricultural residues (for example, wheat straw or sugarcane bagasse), which makes softwood a particularly challenging material for ethanol production.
The Vienna Philharmonic, in its three programs conducted by Daniel Barenboim and Pierre Boulez at Carnegie Hall over the weekend, managed to present a lot of challenging material: substantial works by Arnold Schoenberg in each concert, a piece by Anton Webern, another by Mr. Boulez.
Batty is a master at presenting challenging material in 'gentle though rigorous' ways, judiciously combining text, graphics, and notation, and moving from easy-to-grasp toy problems to real examples.
While it is still early in the show's run (it continues through Aug. 4), the numbers are encouraging for the armory, which has never before presented a show with such challenging material – videotaped scenes of nudity, plentiful faked violence and explicit sexual acts.
In fact, historically speaking, Victoria isn't that bad, and both Coleman and Rufus Sewell as Melbourne make a good fist of some challenging material.
Automated handling of heavy deformable goods, due to their challenging material properties, sets a benchmark for handling sacks, such as bags of fabrics, synthetic packings, papers filled with coffee, cereals and plastic pellets.
SAGE helps students learn how to study chemistry, provides extra support for the challenging material, and fosters a collaborative and proactive community of learners.
"All I ever wanted to do all the way through was to make a difference," says the US-born filmmaker, explaining how his lifelong passion for social justice was ignited while putting on plays at Harvard and seeing how an audience reacted to serious and challenging material.
Bob Gersh, co-president of the Gersh Agency, which represents the likes of David Schwimmer and Twilight star Kristen Stewart, says that a lot of the "most interesting and challenging material out there" is being made for the small screen.
Although Thetford Forest wood is generally regarded as a challenging construction material, the team decided to source 70% of the wood used for the building from there.
