[单选题]
A vibration generator with a frequency of 5Hz/0 /sot:y1t/ooug qav produces a travelli :91t xgp/605p ctr-znvoxyedng wave in a string. The graph shows how displacement of particles in the string varieoe t/6vr xtx-z9 c g0yp1p:5dns 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 $cms^{-1}$
