Two neighboring network nodes, where Node A is transmitting data packets and node $Bi$

receiving them, use a sliding$-$window protocol as shown below What should the value $x$

in the last RR message?

a$.3$

b$.2$

c$.1$

d$.4$

$($B$1)$

$($A$1)$

$($A$2)$

$($A$3)$

a b c d e f ghij

$($A$4)$

$($B$2)($B$3)$

$($B$4)$

$($B$5)$