[单选题]
A vibration generator with a frequm5g/co -aigx e+up(4tency of 5Hz produces pkds*6 cr*mn:bwfd2ruf4 * kyb-1 z9da travelling wave in a string. The graph shows how displacement of pars1b2p fzuw:d-b*k 9frc *6d*m 4nrdykticles 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 $cms^{-1}$
