What is the logic gate with one input and one output?

How many $NAND$ gates are required to form an $AND$ gate?

The following figure $(i)$ shows a logic gate circuit with two inputs $A$ and $B$ and output $C$. The voltage waveforms of $A, B$,and $C$ are as shown in the figure $(ii)$ given below. The logic circuit gate is:

In the logic circuit given,$A, B$ and $C$ are the inputs and $Y$ is the output. The output $Y$ is $HIGH$ when:

In the given circuit,find the value of $Y$.

In the logic circuit diagram, when all the four inputs, $A, B, C, D$ are 'one' the outputs $Y_1, Y_2, Y_3$ are respectively $(1, 1, 0)$. When the inputs $A$ and $C$ are changed to zero and $B$ and $D$ are still 'one',then the outputs $Y_1, Y_2, Y_3$ are respectively change to