$seq1=ABCDEFGH;$seq2=substr($seq1,2,3);执行以上语句后，$seq2=？
举一反三
- 假设conn为数据库连接对象，下面哪条语句可向表TeacherInfo中添加变长字符串类型的Name列 A: seq="INSERTINTOTABLETeacherInfoADDNameVARCHAR(50)"conn.execute(seq) B: seq="ALTERTABLETeacherInfoADDNameVARCHAR(50)"conn.execute(seq) C: seq="ALTERTABLETeacherInfoADDNameVARCHAR(50)"conn.commit(seq) D: seq="INSERTINTOTABLETeacherInfoADDNameVARCHAR(50)"conn.commit(seq)
- TCP连接建立的过程通过双方的报文传输实现，请给出以下报文的发送顺序(1) SYN = 1, ACK = 1, seq = y, ack= x + 1(2) ACK = 1, seq = x + 1, ack = y + 1(3) SYN = 1, seq = x A: (3)(2)(1) B: (3)(1)(2) C: (1)(2)(3) D: (2)(3)(1)
- 用seq函数，生成向量X= (1,2,3,4,5,6,7,8,9,10)的命令是 A: X<-seq[1:10] B: X<-seq(1, by = 1, length.out = 1) C: X<-seq(1, by = 10, length.out = 1) D: X<-seq(1, by = 1, length.out = 10)
- 主机甲向主机乙发送一个(SYN=1,seq=1)的TCP报文段,期望与主机乙建立TCP连接,若主机乙接受该连接请求,则主机乙向主机甲发送的正确的TCP报文可能是:( <br/>) A: (SYN=0,ACK=0,seq=1,ack=2) B: (SYN=1,ACK=1,seq=0,ack=2) C: (SYN=1,ACK=1,seq=1,ack=0) D: (SYN=0,ACK=0,seq=0,ack=2)
- 中国大学MOOC: TCP连接建立的过程通过双方的报文传输实现，请给出以下报文的发送顺序(1) SYN = 1, ACK = 1, seq = y, ack= x + 1(2) ACK = 1, seq = x + 1, ack = y + 1(3) SYN = 1, seq = x