Sound propagates through tissue as a sequence of which two phenomena?

• A. Compressions and Rarefactions
• B. Reflections and Refractions
• C. Vibrations and Oscillations
• D. Doppler shifts and Echoes

Answer: (A)

Sound moving through tissue is a longitudinal wave, which propagates as a repeating sequence of compressions and rarefactions. As the wave travels, tissue particles oscillate along the direction of travel: compressions are regions where particles are pushed closer together, creating higher pressure, and rarefactions are where they spread apart, creating lower pressure. This alternating pattern carries the sound energy through the medium.

Other options describe interactions or different phenomena, not the fundamental propagation pattern. Reflections and refractions are about how waves change direction at boundaries, not the inherent sequence of pressure changes. Vibrations and oscillations are general motions and don’t specify the alternating high- and low-pressure regions. Doppler shifts and echoes relate to frequency changes and signal returns, not the basic way sound propagates as compressions and rarefactions.