$3\mathrm{.}06.$a$\mathrm{.}4$ The RDT $3\mathrm{.}0$ protocol $($d$).$ Consider $($yet again$)$ the rdt$3\mathrm{.}0$ protocol and now the new$/$different operation of the rdt$3\mathrm{.}0$ protocol shown below. In this diagram, we have intentionally left out the sequence numbers and ACK numbers in the packets sent by rdt$3\mathrm{.}0($that$\text{'}$s what we'll ask about in this question$).$

What is the sequence number on the packet sent by the sender at time t$4?($Note: there is only one correct answer below$).$

Group of answer choices

There is no sequence number used on this packet.

$2$

$0$

$1$