[单选题]
A coherent light is incident on
cmw ujlgzqk x/kz3ql,(;;/e 8 a double slit that has slit
+emkp7 ;q0 t:/kpk6 tli*qibu 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?