[单选题]
A vibration generator with a freg2 bc ffv;s jhsb52/:jquenc0dkjlufvbvnq.t h- 4i;9 dy1p2gs+e 2 y of 5Hz produces a travelling wave in a string. The graph shows how displq +v201.h-vd;djl9usi nk4 2bp eg ytfacement of particles in the string varies with the distance from the source.
What is the wavelength and the speed of the wave?
A. Wavelength 5cm;Speed 25 $cms^{-1}$
B. Wavelength 5cm;Speed 1 $cms^{-1}$
C. Wavelength 5mm;Speed 25 $cms^{-1}$
D. Wavelength 5mm;Speed 1 $cms^{-1}$
