[单选题]
A vibration generator with a - lpi/y :a;sdaascrb4ee: :6zfrequency of 5Hz produces a travelling wave i:vzfeo,bb2- iurx/ 6n qe--zm n a string. The graph shows how displacement of particles: nmb z6x-r e qo,zb--2vfuei/ 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 $cms^{-1}$
