[单选题]
A coherent light is incident on a
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yl- lz.+kxgn6slit that has slit separation of $d$ and slit width of $b$. An interference pattern on a screen is observed. The graph shows the variation of intensity with distance from the centre of the pattern.
$S_1$, $S_2$ and $S_3$ are the separations between various points on the pattern and the center of the pattern. The distance between the screen and slits is $D$. What is the wavelength of the incident light?
