A 3-input majority logic gate has inputs $X, Y$ and $Z$. The output $F$ of the gate is logic ' 1 ' if two or more of the inputs are logic ' 1 '. The output $F$ is logic ' 0 ' if two or more of the inputs are logic '0'. Which one of the following options is a Boolean expression of the output $F$ ?

For the circuit shown below, the propagation delay of each NAND gate is 1 ns. The critical path delay, in ns, is __________ (rounded off to the nearest integer).

The output of the combinational circuit given below is

The minimum number of 2-input NAND gates required to implement a 2-input XOR gate is