Identify the gate structure

The given options suggest the circuit is one of the basic diode/transistor logic combinations.

At the output stage $Y$, the relation corresponding to a NOR-type inversion of OR inputs is: $Y = \overline{A+B}$

Apply De Morgan’s law

Using De Morgan’s theorem: $\overline{A+B}=\overline A\,\overline B$

Match with the given options

• A: $A.B$
• B: $\overline A + \overline B$
• C: $\overline A.\overline B$
• D: $A+B$

Therefore, $Y=\overline A\,\overline B$

Correct option

Hence the correct answer is: $\boxed{\text{C}}$