Interference in light waves:

A. can only be constructive in nature.
B. can only be destructive in nature.
C. doesn't exist; light waves cannot interfere with themselves because there is no medium.
D. can produce bright and dark patterns through a slit.
E. can only occur between different frequencies of light.

D. can produce bright and dark patterns through a slit

Explanation:

Interference in any type of wave can get in two forms, constructive interference, and destructive interference.

The constructive interference is between two waves with the same phase, that is, each crest and trough correspond with the crest and trough of the other, getting as result a wave with twice the amplitude of the original one.

The destructive interference is between two waves out of phase and with the same amplitude. In which the crest of one cancels with the trough of the other.

If light passes through a slit it will get a diffraction pattern in a screen, at which each bright pattern corresponds to a crest, a dark pattern to a trough, as a consequence of constructive interference and destructive interference in different points of its propagation to the screen.  

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