answer the following questions according to the description below

if you have $4$ GPRs $($R$0-$R$3)$ and the two specail purpose registers $($MAR$,$ IR$),$ and the ALU can perform $($addition$,$ subtraction, multiplication$).$ if the instruction to be executed is add R$1,$R$2,$R$3($R$1+$R$2=>$R$3)$ and three bus organization is used.

answer the following questions.

when horizontal implementation is used, the number of bits needed to implement the ALU in the microinstruction format is

$*$

$5$

$6$

$4$

$3$

when vertical implementation is used, the number of bits needed to implement the ALU in the microinstruction format is

$*$

$3$ bits

$2$ bits

$7$ bits

$5$ bits

$4$ bits

when vertical implementation is used, the number of bits needed to implement the source$2$ in the microinstruction format is

$*$

$7$ bits

$4$ bits

$3$ bits

$5$ bits

$2$ bits

when horizontal implementation is used, the number of bits needed to implement the source$1$ in the microinstruction format is

$*$

$4$

$6$

$5$

$3$