TCP 发建立连接请求时,需要将下面哪个标志位置位 ___ A. ACK @font-face { font-family: 宋体; }@font-face { font-family: 宋体; }@font-face { font-family: "@宋体"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: "Times New Roman", "serif"; }.MsoChpDefault { font-size: 10pt; }div.WordSection1 { } B. SYN @font-face { font-family: 宋体; }@font-face { font-family: 宋体; }@font-face { font-family: "@宋体"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: "Times New Roman", "serif"; }.MsoChpDefault { font-size: 10pt; }div.WordSection1 { } C. FIN @font-face { font-family: 宋体; }@font-face { font-family: 宋体; }@font-face { font-family: "@宋体"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: "Times New Roman", "serif"; }.MsoChpDefault { font-size: 10pt; }div.WordSection1 { } D. PSH @font-face { font-family: 宋体; }@font-face { font-family: 宋体; }@font-face { font-family: "@宋体"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: "Times New Roman", "serif"; }.MsoChpDefault { font-size: 10pt; }div.WordSection1 { }