The image below is a sketch of two-slit diffraction of light. Narrow slits at A and B act as wave sources, and waves interfering in various phases are shown at C, D, E, and F. A sketch of two-slit diffraction of light. Narrow slits at A and B act as sources on the left, and waves interfering in various phases are shown at C, D, E, and F on the right.

The equation for the double-slit experiment for small angles is

Equation showing lambda divided by d equals x divided by L

In the image, which description below represents the d of the equation?

The distance between A and B
The distance between A and D
The distance between midpoints D, E, and F
The light bands between D and E and F