tropopause

"...approximately 60 beats per minute."

"The geologist studied the stratosphere exposed in the road cut, carefully examining the layers of sediment for clues about the region's history. "

"The fence marks the boundary between the park and my neighbor's yard. "

"Airplanes fly people across countries for vacations and business trips. "

"It was an experience he would not soon forget."

"The airplane experienced some turbulence on the flight, causing a few passengers to feel uneasy. "

"The teacher tried to temperate the students' excitement before the field trip so they would listen to the safety instructions. "

"As the altitude increases, the temperature gets lower, so remember to bring warm clothes to the mountains."

"Planes typically fly in the lower part of the troposphere, where the weather changes rapidly. "

"The transition from elementary school to middle school was difficult for many students. "

"The school is two kilometers from my house, so I usually take the bus. "

"My brother normally gets up early for school. "