$2.$ Simulate your design.Unit $1-$ Design a $4-$bit adder$/$subtractor that accepts two $4-$bits numbers, A and B$,$ andeither add them up $($A $+$ B$)$ or subtract them $($A B$)$ depending on a control signal A$/$S$($when the control signal is $0$ perform ADD, otherwise if the signal is $1$ then performSUB$).$ The result will be stored in C$.$Unit $2-$ Design a $4-$bit AND$/$OR unit that accepts two $4-$bits numbers, A and B$,$ andeither AND them or OR them depending on a control signal A$/$O $($when the controlsignal is $0$ perform AND, otherwise if the signal is $1$ then perform OR bitwise logicaloperation$).$ The result will be stored in C$.$Unit $3-$ Design three $4-$bit parallel registers to hold A$,$ B$,$ and C where C keeps theoutput of the ALU. The registers have a R$/$W control signal that indicates that they arebeing written to or read from.Please provide photo of loogisim circuit