Correct Answer - C
The gate circuit can be shown by given two inputs A and B.
Output of NOR gate, `Y_(1)=bar(A+B)`
Output of NAND gate, `Y_(2)= bar(Y_(1)*Y_(1))=bar (bar(A+B)*bar(A+B))`
`=barbar(A+B) +barbar(A+B)`
`=(A+B)+(A+B)=A+B`
Output of NOT gate, `Y=bar(Y_(2))=bar(A+B)`
which is the output of NOR gate.