For which gate is the output high,if at least one input is low?

To get an output $Y = 1$ in the given circuit,which of the following inputs will be correct?

In the Boolean algebra,the expression $\left( {\overline {\bar A \cdot \bar B} } \right) \cdot A$ is equal to:

If ${V}_{A}$ and ${V}_{B}$ are the input voltages (either $5\, V$ or $0\, V$) and ${V}_{0}$ is the output voltage,then the two gates represented in the following circuit $(A)$ and $(B)$ are:

Switch $B$ can rest at either $1$ or $2$,and switch $A$ can rest at either $3$ or $4$. Determine the output expression.

Explain logic gates.