Physics · Sound Waves

Consider the following statements regarding the behavior of ultrasound waves: Statement - I: When an ultrasound wave travels from one medium to another, its wavelength, frequency, and speed all change. Statement - II: The frequency of an ultrasound wave remains unchanged while travelling from one medium to another. Statement - III: The frequency and speed of an ultrasound wave change, but wavelength remains constant when crossing media boundaries. Statement - IV: 'Echocardiography' is a medical diagnostic technique that utilizes ultrasound waves. Which of the following combinations of statements is true?