[单选题]
A vibration generator with a fre+).ibg ycj ylq4/q11qkti cy3quency of 5Hz produces a travelling wave nr(1fq6-s lbpv,u6vtd(/ ch q in a string. The graph shows how displacement of particles in the string varies with the distance from the sout/pv-q rf6 b s, 61qlnvdu(hc(rce.
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 $cms^{-1}$
