Physics - Semiconductors Question with Solution | TestHub

$\mathrm{y}=\overline{(\overline{\mathrm{AB}})\cdot (\overline{\mathrm{CD}})}=\overline{(\overline{\mathrm{A}}+\overline{\mathrm{B}})\cdot (\overline{\mathrm{C}}+\overline{\mathrm{D}})}$

$=\overline{(\overline{\mathrm{A}}+\overline{\mathrm{B}})}+\overline{(\overline{\mathrm{C}}+\overline{\mathrm{D}})}=\mathrm{AB}+\mathrm{CD}$

Hence (D).