During an ultrasound scan (such as obstetric ultrasonography), a water-soluble coupling gel is applied to the patient's skin before placing the transducer. What is the primary physical purpose of this gel?

Options:

• A: To lubricate the skin and prevent friction-induced heating from the high-frequency transducer.
• B: To match the acoustic impedance of the transducer with the skin, preventing the reflection of ultrasound waves at the air-skin boundary.
• C: To act as a chemical catalyst that increases the speed of sound waves as they enter the body.
• D: To polarize the ultrasonic waves so they can penetrate deeper into the soft tissues.

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