indurate

""The group of friends issued playful challenges to each other to see who could build the tallest sandcastle." "

"The scientists repeated the experiment in order to confirm the result."

"After you hand in your essays, I will give both grades and feedback."

"strengthen a muscle"

"The constant noise from the construction site made it hard to concentrate on my homework. "

"The boss was completely unfeeling when he fired Sarah right before the holidays, knowing she had a family to support. "

"Limit your exposure to harsh chemicals.   Get as much exposure to a new language as you can."

"The rubber band was resilient, snapping back to its original length after being stretched. "

"My favorite book is the one about space exploration. "

"The teacher's negative on the project proposal meant we had to revise it completely. "

"The politician received a lot of public criticism for his controversial stance on the issue."

"My little brother was obstinate about wanting a new video game, refusing to consider any other activity. "