A, when the readable period from vibration image b is T=0.4s, the frequency of the wave is f =1t = 2.5hz; It doesn't fit the meaning of the question, so A is wrong.

B, when the wavelength λ=4m is read from the fluctuating image A, the wave velocity is V = λ t = 40.4 =10m/s; B is wrong because it doesn't meet the meaning of the question.

C. According to Figure B, the displacement of the origin O at time t is positive on the Y axis, and the acceleration direction of the origin O is negative on the Y axis according to the fact that the acceleration direction is opposite to the displacement direction; C is wrong because it doesn't meet the meaning of the question.

D, because the propagation direction of the wave is unknown, the vibration direction of the particle cannot be determined, so D is correct.

Therefore, choose: d.