Identify the main reason why doctors prefer ultrasound rather than audible sound waves for imaging internal organs.
(a) Ultrasound waves travel much slower in body tissues, giving clearer echoes
(b) Ultrasound waves are beyond human hearing, so patients do not feel any discomfort
(c) Ultrasound waves have shorter wavelengths, allowing them to resolve small structures
(d) Ultrasound waves have longer wavelengths, so they can bend around organs and reach deeper parts