$3.(20$ pts$)$ Choose the most appropriate answer in each of the following cases $($with a brief justification$).$

D: To implement packet re$-$transmissions in a window$-$based data transfer protocol $($with window$-$size Ws $>1),$ the $$selective$-$repeat$$ policy $($SR$)$ incurs a higher software complexity than the $$goback$-$N$$ policy $($GBN$),$ because:

$($i$)$ Maximum allowed Ws in SR is only half of that in GBN;

$($ii$)$ SR treats each of Ws packets separately, but GBN treats the entire Ws packets as one unit;

$($iii$)$ SR reduces unnecessary packet retransmissions, when compared to GBN;

$($iv$)$ Retransmission timeout in SR is more sensitive to network transfer delays than in GBN$.$