tough

"The temperature in the room dropped nearly 20 degrees; it went from hot to cold."

"The children physically exhausted themselves playing tag in the park. "

"One way to encourage your employees to work harder is by giving them incentives."

"The subway train is undergoing a tunnel underneath the city. "

"The student's opposition to the new school rules caused a disruption. "

"While walking in the park, I encountered an old friend I hadn't seen in years. "

"The metal rod showed a noticeable deformation after the hammering. "

"The union negotiator met with the company representatives to discuss wages. "

"He threatened me with a knife."

"My sister's reputation for being organized helped her excel in school. "

"The difficult training regime is toughening the athletes for the upcoming competition. "

"We challenged the boys next door to a game of football."