(1)A: Because the velocity image is a sine (cosine) function, and the kinetic energy is the square of the velocity, that is, the square of the sine (cosine) function, its period becomes half of the original, so A is wrong.

B: According to Einstein's equation of mass and energy, the mass of an object in motion is greater than that at rest, so B is wrong.

C: As long as it is a wave, it can interfere and diffract, so C is correct.

D: binary number transmitted by computer technology: 0,1; 0, 1 can be expressed by laser flicker; So it can be used to convey information, so D is correct.

So choose: CD

(2) Make a light path diagram according to the refraction law, as shown in the following figure:

Because the upper and lower surfaces are parallel, when the two surfaces refract, the refraction angle of the first refraction is the incident angle of the second refraction. According to the law of refraction, the incident angle of the first refraction is equal to the refraction angle of the second refraction, so the outgoing rays should be parallel.

According to the fact that the optical path is reversible, because the two interfaces are parallel, they can enter and exit, that is, if the incident direction of parallel light is adjusted, the light cannot be totally reflected on the lower surface.

(3) The blade vibrates completely for 20 times per minute, with a period T=6020=3s.

When blade A is at the peak, blade B is at the trough, and there is a peak between two blades, then the distance between two points AB is 1.5 wavelength, that is, 1.5λ= 18m, λ= 12m.

From: v=λT:

v= 123=4m/s

So the answer is: (1) CD; (2) parallel; No; (3) 4 meters per second