ultrasonic

"The train engineer blew the whistle, signaling the start of the journey. "

"Humans share common ancestors with other apes."

"The fire emits heat and smoke. "

"The hikers walked along the entire mountain range. "

"Humans share common ancestors with other apes."

"The teacher encouraged the students to explore the beyond of current knowledge in science. "

"The frequency of bus service has been improved from one every 15 to one every 12 minutes."

"The balloon rose high in the sky.   The wall was high.   a high mountain"

"The acoustics in the concert hall were so good that every note sounded clear and vibrant. "

"The only perceptible was the faint sound of the clock ticking in the otherwise silent room. "

"He was safe and sound."

"The radio station broadcasts at a frequency of 980 kilohertz. "