In order to demonstrate the interference of light waves, the light source emits rays of light, which towards the double slit.
a. refract
b. reflect
c. go straight
d. diffract

D. Diffract

Explanation:

Diffraction is a phenomenon that is based on the deviation of the waves (light waves in this case) when encountering an obstacle.

In addition, it is important to note this phenomenom occurs in all types of waves (ncluding electromagnetic waves).

So, in a general way:

Diffraction happens when a wave (mechanical or electromagnetic wave) meets an obstacle or a slit . When this occurs, the wave bends around the corners of the obstacle or passes through the opening of the slit that acts as an obstacle.

Hence, the correct option is D: