In TCP protocol, a receiver is waiting for a segment with sequence number $\backslash (=60\backslash ).$ However, receiver receives two segment with same data size $\backslash (=20\backslash )$ bytes including Sequence Number $\backslash (=60\backslash )$ and Sequence Number $\backslash (=80\backslash )$ respectively at the same time. What will receiver do next?

Sending back to sender a segment including ACK$=120$

Sending back to sender a segment including ACK$=100$

Sending back to sender a segment including ACK$=600$

Sending back to sender a segment including $\backslash ($ A C K$=80\backslash )$