Complete the sentence with the right option.

To reflect the sound waves from any surface, the surface should have dimensions ____________.

During reflection, sound waves obey the law of reflection. 
To have an appreciable reflection of a sound wave from any surface, it should have a dimension equal to or greater than the wavelength of a sound wave falling on it. 
That is, a smaller object will not reflect the sound waves of a larger wavelength.

Therefore, 'equal to or greater than the wavelength of a sound wave' is the correct response.