[单选题]
A vibration generator with a frequency geeblo;*j1z wr 4u1 zg(.pxn4 o42m xse(j3la nf 5Hz produces a travelling wave in a string. The graph shows how displacement of particles in the string varies with the distance from the43xla2n(smj e 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 $cms^{-1}$
