Task: Class Definition Understanding (ontology: Earth_Environment/EnvironmentOntology)

Which of the following definitions best describes 'ultrasound radiation'?

A. An acoustic radiation process during which waves that transmit sound energy at frequencies above 20 kHz are emitted by a source.
B. An infrared radiation during which waves with frequencies between 30 THz and 120 THz and with wavelengths between 10 micrometers and 2.5 micrometers are emitted by a source.
C. Soil which has increased levels of chalk.
D. Sound which is lower in frequency than 20 Hertz, or cycles per second.

Answer: An acoustic radiation process during which waves that transmit sound energy at frequencies above 20 kHz are emitted by a source.