GATE EC 2024 Set 1 Q30 — Combinatorial Circuits

​​​​​A $4$-bit priority encoder has inputs $D_{3}, D_{2}, D_{1}$, and $D_{0}$ in descending order of priority. The two-bit output $A B$ is generated as $00,01,10$, and 11 corresponding to inputs $D_{3}, D_{2}, D_{1}$, and $D_{0}$, respectively. The Boolean expression of the output bit $B$ is $\_\_\_\_\_\_\_$.