Which one of the following statements is not correct?

Answer options

1. AUltrasonic waves cannot get reflected, refracted or absorbed.
2. B Ultrasonic waves are used to detect the presence of defects like cracks, porstty, etc. in the internal structure of common structure materials.
3. CUltrasonic waves can be used for making holes in very hard materials like diamond.
4. DUltrasonic waves cannot travel through vacuum.