System B sends a SYN/ACK packet to victim

TCP SYN Flood attack uses the three-way handshake mechanism.
1. An attacker at system A sends a SYN packet to victim at system B.
2. System B sends a SYN/ACK packet to victim A.
3. As a normal three-way handshake mechanism system A should send an ACK packet to system
B, however, system A does not send an ACK packet to system B. In this case client B is waiting
for an ACK packet from client A.
This status of client B is called _________________

A.
“half-closed”

B.
“half open”

C.
“full-open”

D.
“xmas-open”