17. What kind of wave require a medium to travel through?
A. mechanical wave
B. electromagnetic wave
C. microwave
D. radio wave
18. is a substance or material through which a wave can propagate or produce A structure
B. medium
C. object
D. body
19. What is the lowest point of a wave? A. amplitude
B. trough
C. crest
D. wavelength
20. It is the height of a wave and also measures its intensity.
A. crest
B. frequency
C. amplitude
D. trough​