When going round a corner your direction changes which means your velocity changes which means there is an acceleration.
' A ' is one crest of the wave. After every wavelength, there's another one.
' B ' . . . the vertical arrow under B shows the amplitude of the wave
' C ' is one trough of the wave. After every wavelength, there's another one.
' D ' . . . the horizontal arrow over D shows the wavelength.
I would say your answer is B, since Newton's 3rd law is, "For every action, there is an equal and opposite reaction."
It's talking about pairs of actions. Sorry if I'm wrong.
