Dim s As Double, x As Double, n As Integer, i As Integer

s=0:n=0

For i= 1 to 4

  n=n+1

  x=(n-1)/(n+1)

  s=s+x

Next i

该程序段计算的数学表达式是（   ）

Private Sub Command1_Click()

        Dim  N  As  Integer

        Dim  S  As  Integer

        N = val(Text1.Text)    

        S = 0

          For i = 1 To N

             S = S +  i * (i + 1)

          Next i

        Text2.Text = str(S)

End Sub

①输入输出框 ②连接框 ③流程线 ④判断框 ⑤处理框 ⑥开始结束符

A~F六种流程图符号代表的含义依次是{#blank#}1{#/blank#}  

①将A杯中的酒倒入C杯②将B杯中的醋倒入A杯③将C杯中的酒倒入B杯中